Demystifying Trailing

Jul 15, 2019

By Deborah Palman,

Maine Warden Service, ret.

In my 40 plus years of dog training experience, I’ve had the good fortune to work in a variety of dog training areas in sport and practical disciplines, plus 30 years of working dogs as a first responder in search and rescue.  After retirement, I’ve gone on to continue work as a volunteer wilderness search and rescue and human remains detection team handler, so I’m still active in these areas. I also teach seminars in scent related disciplines, and each time I teach a seminar, I consider again how to get the points across that allow others to design efficient and effective training programs.

In the last few years, as I trained new narcotics teams and reviewed the training steps to produce an operational narcotics detector team, I realized that teaching a dog to find a person by trailing requires the same basic training steps used to train all detector dogs, no matter what the target scent is.  The problems most trailing dog handlers encounter is that many of them don’t have these steps in mind when they train. They do what people traditionally have done in their training group to teach trailing. But the only differences between what a narcotics detection team does and what a trailing dog team does are the target odors they are looking for, the environments they work in, and the fact that the trailing dog team follows “residual” target odor that is left on the ground to the the target instead of following air born target odor to the target.  


Tracking vs. Trailing


Some police K-9 handlers, sport dog handlers and the public use the word “tracking” when they describe a dog or a person following the scent or sign left behind when a person travels over the ground.  “Trailing” is the term used by bloodhound and search and rescue handlers and trainers who know that teaching a dog to “scent discriminate” or follow one target person’s scent only (often utilizing a target scent article) is one of the first steps needed to produce a dog that will be the most effective in finding a person.  These handlers and trainers also aren’t hung up on the idea that the dog needs to follow the “footsteps” on the ground. Allowing the dog to use its natural, inbred talents to locate the target scent means the dog doesn’t always follow the footsteps, but follows the scent. 

Having worked in both areas for years, watched tracking and trailing teams work, seen their relative effectiveness in finding people at actual police and search and rescue scenes, and having trained my own tracking and trailing dogs, I am now firmly in the trailing camp with my training.  I’ve done sport tracking and “tweaked” my practical trailing work enough to pass sport tracking tests with my search and rescue trailing dogs, but I know that the better bloodhound handlers and trainers have it right: If you haven’t taught scent discrimination to your trailing dog, don’t expect consistent success at search and rescue scenes or other real life trailing (or tracking) situations.  So instead of playing word games with tracking and trailing, I am going to just use the word trailing. Trailing means scent discriminating, and scent discriminating is one of the essential steps needed in teaching a detection dog.  

Trailing is Detection

The first step in training a detection dog is to establish a reward system.  Dogs work for food, for play, for toys and some detection dogs with high hunt drive work just to “hunt” and follow the scent puzzle to its conclusion.  Trailing dogs can be taught with any reward system, but the important point is that the reward has to motivate the dog to work. What ever the reward, the dog will be “imprinted” on the target scent by linking the reward to the target scent in the dog’s mind.  What is the target scent in trailing? The scent of the person the dog is working to find on that trail. What is the target scent in narcotics? Whatever narcotics scent(s) the dog is working on that day. In narcotics, trainers will use a different systems and pieces of equipment to try to introduce the narcotics odor in a manner that doesn’t tie other environmental or handler cues to the odor, like scent boxes, walls with holes, etc.  Or they may use a scented toy to introduce odor and then train the dog not to indicate on the scent of “unscented” toys.  

Since the primary motivator of trailing dogs is usually a person running away with the dog’s toy or food, the person is the target scent and motivator all in one, and it usually doesn’t take much work to get the dog to understand the hunting game.  What takes more time is teaching scent discrimination and eliminating the other cues (like a running or visible person and handler influences) from information the dog uses to solve the detection problem.


Scent Discrimination


Once a dog is imprinted on one or more odors and has an understanding that “odor = target = reward,” scent discrimination work needs to be done.  This should be done before the dog is taught a “finished and proofed” indication, or an indication on an incorrect odor becomes hard to change if it shows up later in the dog’s performance.  Up to this point, even if a program uses equipment that helps to separate outside influences from the introduction of target odor, the dog has to learn that not every odor produces a reward. In the imprinting stage, usually the target odor is the only “unusual” odor presented to the dog at that time.  Scent discrimination in narcotics training means introducing many other odors to the dog besides the target odors, like odors that might be used for masking, common chemicals and odors found in search areas, odors that are found on the packaging of the drugs, etc., and showing the dog that these are odors that are NOT going to be rewarded.  For example, if, in training, drugs are packaged in a PVC pipe, the dog is likely to indicate on PVC pipes without drugs unless the dog has been trained that the PVC pipes alone don’t produce any rewards.  

All training in scent discrimination has to rely on the dog’s choice and whether or not that choice is rewarded or not.  Yes, you could teach a dog to not indicate on PVC pipes without drugs by telling the dog “no” or causing the dog discomfort in some manner when it indicated on PVC pipes, but this will probably cause the dog to avoid all PVC pipes, even the ones that contain drugs.  Much of detector training is scent discrimination training: setting up endless choices of odors to choose from and rewarding the correct choices and ignoring the wrong ones.  


No Help Allowed


In detection training, all the training needs to be formulated so that the handler and/or trainers give no “help” to the dog.  Dogs are masters at reading body language and noticing split second changes in their environment. They notice everything about the people around them: their body language, their heartbeat and even their smell.  Even with elaborate equipment, it is hard to eliminate all the signals given off by the people present, and advanced training needs to include having the handlers and trainers giving off conflicting signals, like trying to pull the dog away from target odor.  The point is that, again, all training has to rely on the dog making the right choice without any help from the humans involved, whether or not that help is produced consciously or unconsciously.  


Scent Discrimination in Trailing


So how does one teach scent discrimination in trailing?  Generally dogs that are taught trailing by seeing a person leave don’t have a problem with scents unrelated to humans in the initial training that is all short and fresh trails.  But they need to be taught to follow the target person and not other people. This is started by introducing a scent article with the target scent during the imprinting exercises.  In the beginning exercises, the traillayer drops a scent article at the location the dog is to start the trail. Dogs naturally will sniff this article because it stands out from the environment, so the dog pauses only a second to check the article then continues on the trail to find the traillayer and get a reward.  As time goes on and the dog is taught a starting ritual for trailing, the article will be moved from the ground in a series of steps so that it can be presented by the handler at the start of the trail. But leaving it at the start of the first few run away trails is the first step.

It is about this point that some police K-9 handlers who have been tracking and not trailing begin to whine about not having a scent article to start all their tracks.  This is not a valid argument because all tracks or trails start with some sort of target scent, or the dog would not be trailing. The target scent may be a car seat, it may be a broken window at a burglary, or it may just be a “point last seen” where the dog can pick up a relatively uncontaminated scent that leaves the area.  Not all “scent articles” are contained in a bag. The handler has to determine how they will present the target scent to the dog, or they may have to rely on the dog to pick up the scent. If you want more information on starting tracks, my article “The Start is the Most Difficult Part,” as well as a number of other articles on trailing, are available on the Maine Search and Rescue Dog web site ( under “Search and Rescue Literature.”  The crucial point is that the handler knows how to present the target scent to the dog when starting a trail.  If the dog’s trail is important to a criminal investigation, the handler has to be able to articulate how they set the dog on the target scent in a court of law, whether or not they use an actual “scent article.”  

Scent discrimination in trailing is taught using “splits.”  In split trails, two traillayers walk side by side for 100 feet or so, then split off at 45 degree angles or more, walking a short distance to a hiding place.  Like all basic trailing exercises, the set up has to be so that the beginner dog isn’t unduly influenced by wind blowing from the traillayer or by visual cues that can help or mislead the dog.  The target traillayer has left a scent article at the start or in a bag with the handler. The handler can shake the article out on the ground at the start, or start from the bag if the dog is ready for this step.  Just like narcotics training, the dog is allowed to make a choice at the split and is rewarded if it trails to the correct traillayer, and given nothing if it trails to the wrong person. If the dog trails to the wrong person, the handler takes the dog back to the beginning, starts over and, most of the time, the dog will pick the right person the second time.  These are short, because the dog has to make the choice and go to the end of the trail before it gets a reward, or the dog does a “do over” if it made the wrong choice. Of course, this assumes that the tracklayers are of “equal” value to the dog, and not a combination of a person the dog knows really well and lives with and a total stranger. Don’t try to get a beginner dog to pick a total stranger over someone the dog knows and likes. 

Again, it is important that the dog makes the choice and the handler NOT interfere by steering the dog at the split or giving the dog any information until the dog reaches the traillayer.  Narcotics dog handlers know they shouldn’t steer their dog to the drugs, and trailing dog handlers should do the same. These split tracks are done with two people until the dog picks the right track all the time, then done with three or more people until the dog is correct all the time.

Dogs pick this exercise up pretty quickly when it is done correctly.  And once they get it, they don’t seem to forget it. It usually makes sense to them to follow one person.  Teaching scent discrimination correctly also corrects the problem of tracking dogs picking a track based on age – like police dogs that might track the officers that contaminated the scene rather than the suspect.  Once taught scent discrimination, the age of the trail becomes much less important to the dog. They just try to follow the correct scent, and are less likely to make choices based on the age of the trail. Any dog that tracks or trails consistently well under all sorts of conditions involving contamination has learned to scent discriminate, whether or not the handler or training program deliberately included it in their exercises.  Even with less thought out programs, some dogs just understand from the beginning and do a good job. Other teams struggle because some training element has been left out.

When the dog is scent discriminating, trails can be laid in contaminated areas, and the only “contamination” that complicates training is “same scent” contamination by the person laying the trail.  For example, handlers and trainers need to pay attention to where the traillayer has been in at least the last 24 hours and not start new dogs in places where the traillayer has previously been if they expect the dog to start cleanly.  This is why I always pick start points a distance from where the group is parked or has been walking their dogs. More than one time I have tried to start a track from a pole or sign only to find out that the traillayer walked his dog there an hour before I tried to start trailing in the same spot, creating a giant scent “snarl” that was difficult for the dog to sort out, and leaving me wondering why my dog did not start well.

Narcotics detection dogs that are not taught scent discrimination early in their detection training are prone to indicating on novel scents they encounter, or to indicating on scents that accompanied the target scent in training.  Tracking dogs that don’t scent discriminate will switch tracks from one person to another, or pick tracks based on the age of the track. This is common with police K-9 teams who don’t have enough time to train trailing correctly or don’t plan their tracks adequately.  Since the scent that trailing dogs follow can remain in the environment for days or even a week or more, nearly every training venue police K-9 teams practice in has human scent contamination, even if the handler didn’t see someone walking there the last few hours. If the only training tracks a police K-9 does are ones where a scent article is not used, scent discrimination is not practiced and someone walks off and hides within the last 30 minutes, the handler may be programing the dog to follow the freshest track in the area instead of following a specific individual.


Teaching an Indication


All trailing dogs should be taught some sort of end indication to tell the handler that they have found the traillayer.  While “scent lineups” may be controversial, and it is very hard to teach a dog to consistently pick the right person out of a true line up of a number of people (for reasons I can’t go into right now), it isn’t hard to teach a dog to indicate on the person at the end of a trail.  It is also not hard to teach a dog pick the right person out of a few passive people at the end of a trail. This has a number of applications for criminal work, and it can help a team know if they are trailing the right person or not. It also serves as a definitive way to have the dog end the track and close the distance to the tracklayer.  I know that closing in on the traillayer may not be tactically desirable in all situations and that it is best that trailing dog be taught what Jeff Shettler calls a “proximity alert,” but I find a good argument for having the dog go to the traillayer to get its reward. I have a war story I tell about a handler I knew who always threw a toy to his dog at the end of a trail and never had the traillayer reward the dog.  Often he threw the toy before the dog closed all the way into the tracklayer. This team was in training before our training group learned how important it was to have a good indication on the traillayer. At one point in their career, the dog trailed up to within 8 feet of a burglar (who the handler never knew was there) at the end of a nighttime track in an area with clumps of dense bushes. The dog got close enough so that knew where the burglar was and waited for his ball to appear.  After the ball didn’t appear, the dog wandered off and began urinating on trees. The handler became frustrated and left, assuming that the dog never had a good track. The handler heard later on from the suspect what happened. Teaching an indication to other detector dogs is a crucial part of their training, and it should be a part of the training of trailing dogs.


Teaching the Dog to Ignore Distractions


All phases of dog training involve teaching the dog to perform behaviors under various degrees of distraction.  Narcotics dogs need to work around food, pets, traffic, etc., and the number of distractions that trailing dogs encounter is endless.  Trailing handlers rarely have any control over what they encounter outdoors on a trail. The basic process for both is the same -introduce distractions in a measured way, ensuring that the dog has adequate motivation to work, and reward the dog when the dog gets by the distractions and performs successfully.


Extending the Search – Teaching the Dog to Search for Longer Time Periods


Once past the the imprinting stage, all detector dog teams need to gain skill at locating targets under more and more challenging circumstances and searching for longer and longer periods of time.  Narcotics dogs need to go from finding a hide every few minutes during their imprinting and reward stages to finding a reward every 15 or 20 minutes, or whatever the expected search time will be for the team.  Trailing dogs go from following a short, fresh trail with a quick reward to working for hours under more difficult conditions.  

Not extending the “nose time” of the dog to at least the average work period the dog will encounter in the field will lead to a dog that gives up or stops working after its nose time has been exceeded, or, if a narcotics dog, to a dog that gives a “false” or non-productive indication.  Trailing dogs may start following a contaminating trail.

One difference between narcotics dogs and trailing dogs is that the narcotics dog spends most of his time searching areas without scent and a trailing dog spends most of his time “in scent” while following the residual scent of the traillayer.  Good trailing dogs become easy to “read” when they are on the trail because they are “in the zone” and happy and relaxed doing a “scent surfing” pattern that leads them down the path of the trail. When they get off the trail, they go into a “oh no, I lost it” body language and may become hectic and agitated as they try to search out the scent again.  The best ones learn to slow down and search carefully for their target scent if they loose it.  

Part of extending the search for trailing dogs is teaching them to search from areas where the trail is not to where the trail is.  Exercises where the dog is allowed to search areas without any target scent that lead into the trail should teach the dog to pick up and follow the trail from all sorts of angles and approaches.  The biggest difficulty any trailing dog has is the hanlder attached to the end of the lead. Which way the handler pulls, how hard the handler pulls, if the handler and lead are lined up with the trail direction, whether or not the handler lets the dog proceed can have a profound effect on how some dogs trail, especially breeds that are not hounds.  So picking up and following tracks have to include all approach and handling variables.

Part of picking up the trail training also has to include teaching to dog to go “forward” on the trail in the direction the tracklayer is moving.  Determining track direction is not something a dog is born with. It has to be learned, but once learned, the dog never seems to forget it.


Extending the Search – Teaching Negatives


Narcotics and other substance detector dog handlers readily understand the idea of running blank or “negative” rooms, areas and vehicles to extend out the dogs’ nose time and to proof the dog against giving an indication based on the handler’s body language or a distracting or novel odor that may be in the area.  They routinely run exercises with clean containers similar to those used to contain the training drugs, with gloves in the area and anything else they can think of that might tempt the dog into making an error. For some reason, however, tracking trainers and handlers don’t understand this concept, although most of the trailing trainers do.  The traditional tracking training method just starts the dog on the track and keeps on going without specifically addressing what the dog should do if there is no target scent to follow. Handlers and trainers seem to assume that if the scent stops, the dog will stop. Unfortunately, this is not always true. Through the process of teaching the initial reward, imprinting and motivational exercises as well as the addition of more difficult tracks, training usually produces the expectation in the dog that the dog has to move forward and search or look for the trail, even if there isn’t a track there.  The dog not stopping when the scent of the trail stops is the trailing dog’s version of a “false” alert. Sometimes trailing handlers will call these “ghost trails” and are totally at a loss as to why the dog goes on. What is really happening is that the dog feels obligated to track when the handler moves forward even if there is nothing there. Teaching the dog what to do when the scent is not present relieves the psychological pressure to move ahead on negatives and corrects this problem. Doing “negatives” in trailing can make profound differences in problems like ghost trails and dogs overshooting corners and not stopping. 

The negatives I teach all my trailing dog teams are a “negative start,” or starting tracks in areas where no target scent is present and having the dog communicate to the handler that no target scent is present (Kevin Kocher’s “No Scent Indication”), and carefully constructed back tracks on trails (walking back on the same outgoing trail and then turning off) that teach the dog to stop going forward if they loose the scent.   


Desensitizing the Dog to the Handler


All narcotics dog handlers know that their body language and search pattern can negatively affect their dog’s performance.  Training seeks to standardize the handler’s behavior and patterns and to desensitize the dog to the handler’s actions, making the dog “obedient to odor” rather than to the handler.  The same process needs to take place with trailing dog teams. Too often the handler misreads the dog and doesn’t let it go forward when the team should, or urges the dog forward when the team shouldn’t be going forward.  A good trailing dog is not highly influenced by its handler, and this is the advantage of having a single purpose hound, which is bred to hunt independent of humans, and of a dog that is not taught extensive control or other functions which require the dog to be attentive to the handler.  Even if the dog is a multi-tasker and obedience trained, handlers can use harnesses and training routines which tell the dog they are the leader and free to move when trailing, and counteract the effects of the dog’s attentiveness to the handler while trailing.  


Working in Different Environments


Trailing dog teams must spend a tremendous amount of time trailing under different environmental conditions.  Every day they work, the weather changes, affecting scent deposition and detectability. Different terrains hold scent differently – a thick grassy area will hold lots of scent and smooth, dry, slick ice will hold none.  Pavement and urban environments create very different scent picture than woods and vegetated surfaces. Vehicle traffic will sweep scent along, winds will blow scent, thermals created by sun heating will move scent – the list of factors that trailing dog teams need to deal with and handlers need to be aware of are endless.  Only by practicing under all sorts of conditions can a dog learn to handle them and a handler know whether or not his dog can detect scent under those conditions. Besides the conditions of the day or moment, the residual scent of the trail is affected by all the conditions that existed during and after the trail was laid. I’ve seen trails “plowed” into the snowbank by snow plows, moved downwind with time by wind and thermal currents, and washed downstream by run off.  The scent is almost always there, but it takes an experienced handler to understand what may have happened to it, and why the dog is going where it is.


A Good Reference


This article is only a rough outline of what needs to be done to teach trailing.  Like any other detector dog training process, there are lots of details and skills that need to be learned. I urge anyone who is interested in trailing to do some research, as there are plenty of books, seminars and good instructors out there that deal with trailing.

Trailing dog handlers looking for a good reference on trailing should pick up How to Train a Police Bloodhound and Scent Discriminating Patrol Dog by Kevin and Robin Kocher.  The book is relatively inexpensive, concise, and gives detailed descriptions of the basics and components of trailing that scent discriminating dog teams need.  There are other good books on trailing by Tracy Bowling and Jeff Schettler.  

Above all, before tracking or trailing training, put some thought into the process and try to imagine the scent picture the dog is dealing with.  Properly trained, dogs have no problem discriminating and following a target scent that is hours old. Trailing training is detector dog training and should follow a system just like other detector training.