As promised, though admittedly delayed (apparently I forgot to schedule the blog to publish and I didn’t notice until now LOL!)…
Car chasing is a dangerous and compulsive behavior for Dex.  We suspect he may have been on a tie-out and I’d guess one of his main forms of entertainment was chasing cars.  Chasing cars let him use some energy, get excited about a game, and gave him something to do–all of these things likely started to change his brain chemistry around cars.  Exercise, fun, and happiness all cue the brain to start releasing endorphines and other “happy” chemicals… so it becomes much like an addiction.  He is compelled to chase the cars because he knows it makes him feel happy–even though now, there is a lot about life that he is happy about.
So, to combat this I need to become a big source of happy.  To do that, I will be using food, which also initiates the release of feel-good brain chemicals.  I am using a mix of counter conditioning and operant conditioning.  Ideally, I’d like to transfer the drive to chase into the drive to tug, but he didn’t come to me loving the tug, so we are working on that.
During the few days before our walks at the park, I’d been working on Dex chasing cars in our yard.  I was able to work most of the cars what went past, but occasionally he could hear/see a car before I did.  So it wasn’t perfect…but I got better.  Essentially as soon as I heard a car, I’d get my string cheese out of my pocket and put it in front of Dex’s nose and then wheel him around to face me.  I know that if I could hear the car, he could as well.  I’d feed as the car passed and until it was out of sight.  Car=cheese, car=cheese.  This whole process is called counter conditioning… I’m working with two non-neutral bits of stimulus–the car (stimulus one) has meaning to the dog, it means something to chase and the cheese (stimulus two) means yum.  I’m going to pair these two stimuli together to change how Dex feels about the car.  Regardless of his behavior, the car will predict the cheese and should hopefully stop the automatic reaction to chase.  I’m not asking anything of him… simply CAR=CHEESE.
During the first part of our first walk, I repeated this counter conditioning.  Every time he noticed a car, the cheese came out.  The first few cars he was over threshold and couldn’t take his focus off the cars to notice the cheese until the cars were going out of sight…but still, he got some cheese while the car was in sight.  After a few cars he began to eat the cheese as the cars passed.  I wasn’t saying his name, making him look at me, or asking for a sit.  When he’s like that he can’t think but he can eat so it was simply car=cheese.
At one point, during the first walk, we were walking through a field which gave me 40yd or 50yd of space between Dex and the cars.  This was far enough that he could still think when a car was around.  So, I started calling his name and rewarding with cheese for looking at me.  I also started rewarding for “sit” at this distance.  This was way further than his threshold so we began walking closer to the street while continuing to make him think to earn the cheese.  It seemed that this moving closer was the ticket to keeping him operant (able to think and respond to cues) even when very close to the cars.  The rest of this walk, I continued to call his name, get him to turn around and reinforce him for turning around as the cars passed.  Requiring the dog to think in order to earn the reward in the presence of the stimulus is operant conditioning work.  This isn’t so much about teaching the dog to feel differently about the stimulus but teaching them that performing other behaviors in the presence of the stimulus will earn them rewards.
While on leash I continued to work on operant conditioning with him.  See a car…”Dex”…he turns around…give cheese…”sit”…he sits…he gets cheese as the car passes.  It really is about creating an alternate behavior as a habit.  Right now his habit is to chase the cars … I’d like the new habit to be looking at me and for the time being sitting (because it’s an incompatible behavior).  I sort of have a feel for when he’s getting over threshold (to be operant) and when that happens I increase space if I can or take a step back to counter conditioning.
This process has to be repeated over and over again to form a new habit, a new chain of behavior.  Right now the sight or sound of a car causes Dex to react with out thinking… it’s habit, muscle memory almost.  It will take time to break a very strong habit…but he’s definitely come along way in just a few leashed walks.