There is a distance for a reactive dog where they can see another dog and not go into total meltdown mode–this may be 15ft or this may be 150ft.  They may stare or focus on the other dog but they don’t respond with a reaction as an immediate response.  This is the distance where handlers need to start working to change the Conditioned Emotional Response (CER).  If you’ve done your homework with creating a new CER, the reactive dog who is well below their threshold should be able to see a dog and not react.   So at 50ft a dog may be reacting and barking his/her head off but at 80ft you’ve done work to create a very relaxed, dog=food connection, that has prevented the dog from staring or focusing at that distance.   From here, the process of bumping the threshold closer and closer begins.
There are many different exercises that can be done to bump the dog’s threshold closer and closer all while keeping the dog sub threshold.  In my opinion, when working with fear-based reactivity, it is in the best interest of the dog to keep them sub-threshold.  Each and every time the dog reacts to the stimuli, chemicals flood their body in response to the reaction. This influx in body chemistry has an effect on the dog for about 10 days–during those 10 days, it is much easier for the dog to have another reaction….which then makes it much easier for the dog to have a reaction for another 10 days…etc.  So, preventing one reaction actually helps prevent future reactions–keeping it subthreshold is doing yourself a favor.
There are a variety of methods to bump up the threshold (decrease the distance before the dog will react).  There are methods that utilize cued behaviors and those that do not use cued behaviors–honestly, I think the more variety (not within one session obviously) the more well rounded the improvements will be.   Using just look at that (LAT) or using just Behavior Adjustment Training (BAT) or using just watch-me (no cool -AT acronym) can leave a dog a little unbalanced in their rehabilitation.
Let’s start by looking at exercises that use cued behaviors to begin to make decreasing the threshold possible.
Look at That (LAT)–Where’s the Doggie?  LAT is a technique that that teaches a dog to look at their trigger in order to get a reward.  This exercise teaches the dog that their trigger means good things happen–it’s not quite classical conditioning (because LAT is an operant behavior  and is often cued later in the training) but we are creating a connection between looking at the trigger and getting a reward.  It conditions the dog to look at the trigger and then look away from the trigger to get a reward–many reactive dogs will first lock in with a stare and that stare increases anxiety/fear until it boils over into a reaction.  If we can get the dog to break the stare on their own (and reward for looking away) we can prevent escalation.
I shaped LAT… when Shayne was below her threshold, when she looked at a dog I clicked and treated (the treat was placed so she had to turn her head away from the dog).  Since she was below threshold she didn’t have trouble looking away from the dog.  We repeated this over and over and over again when she was well below threshold.  When she ‘got’ the game and would look to the dog and look back to me expecting a treat, I began to put the behavior on cue (I don’t always work it using a cue).  More repetitions and she would eventually look for a dog when I cued “look at that!”  So, we went back to our below threshold and began getting closer and closer while playing the LAT game.  It kept her mind busy and kept her thinking and focusing on me and cues which kept her from getting overwhelmed and reacting.  As long as she was working LAT she was able to get closer to a dog than previously without getting stuck staring and eventually reacting.  This became one of her favorite games to play and kept her calm and having fun even in the presence of her triggers.
Watch me–Look at me, not that!   This works by rewarding very heavily looking at the handler and not getting stuck staring at the trigger.  To me it is a little bit more of a management tool than a rehabilitation technique… but I think it can cross over into being both.  You start working below threshold and you move closer to the trigger little by little.   When you notice any bit of the dog start to prepare to react (stiffening, ear flicks, increased respiration rate) you cue the “watch” behavior to stop the reaction in its tracks and then reward for looking away from the trigger.
I start “watch” during bathroom training sessions (no, not that… when I do training sessions in my bathroom because it’s small and boring which makes me that much cooler).  I click/treat for the dog giving me eye contact without a cue.  When it becomes a predictable behavior I start saying “Watch” as the dog looks to me and then I click/treat.  After some rapid repetitions the dog generally starts to get that when I say  “watch” I want eye contact.  Once the dog is 100% responding in the bathroom, I’ll take the training to a living room or some other pretty low distraction environment.  I want to probably do at least 100-200 successful “watch” cues in each environment before moving on to the next one–a long history of reinforcement can be really helpful as you increase the distraction level of the environment.  When your dog can “watch” outside with high distractions that are not his trigger, you can begin to introduce the trigger to the environment at a distance.  During training, you will continue to slowly decrease the distance between the reactive dog and the trigger dog.  Eventually you can use this when encountering a dog on your path in the park.. ask for a solid watch me as you give a wide berth and pass one another.  It doesn’t necessarily change the way the reactive dog feels about the trigger but it can prevent him/her from rehearsing undesired behaviors.
As a bit of a side note, you can also use a hand target in much the same way as the watch me cue.  You can use it to cue a head turn/look away and you can use it as a way to control the head/nose/mouth of the reactive dog while encountering a trigger dog.