Although the reason for pulling and what rules you must teach is the same for all dogs, some dogs are more of a challenge. My own GSP was one of those “super crazy pullers”. The thing to keep in mind is that law of learning applies to all dogs: Dogs Do What Works. In other words, whatever behavior the dog does that results in getting what he wants, even just a tiny bit of it, will be repeated. The more value the dog sees in the desired outcome, the stronger the behavior, even over-riding any equipment that might cause discomfort.
So for training not to pull, the answer is two-fold. First, use equipment that will mechanically and humanely reduce the force of pulling. I prefer something that controls the head like the Halti for strong pullers. Actually a few years ago I switched over to a Newtrix head halter for my dog because he seemed to be more comfortable in it. The mechanics of how it works is different from the Halti. You can find an explanation here: http://www.newtrix.ca/index.cfm?page=ourProducts It’s a little confusing at first learning how to put it on, but once you practice and follow the directions carefully, it’s not hard.
The second and more important point is to recognize how you are inadvertently reinforcing your dog for pulling. If you take even a single step forward while your dog pulls, he learns that pulling works. Going forward to explore the environment is the most powerful reinforcer there is. It was sure more powerful to my GSP than grilled steak when we were outside.
In training not to pull, the key is to teach your dog that the fastest and ONLY way to move forward is to turn toward you to make the leash loosen so that he feels absolutely no tension whatsoever on his collar, halter or harness. Then and only then will you allow him to continue forward. As soon as the leash tightens again stop and plant your feet so he is unable to take another step forward. This rule has to be black and white, not fuzzy where sometimes pulling works and sometimes it doesn’t. You will have to suspend your walks to really entrench this new rule into your dog’s brain. (Think about how hard it can be for us humans to break a bad habit.)
I used a clicker to mark (click) the precise moment my dog turned toward me to loosen the leash. Then I said “Let’s Go” and took a few fast steps forward until the leash tightened again. (Be very careful if using a Halti or Gentle Leader that can turn the dog’s head. Don’t let the head whip around if the dog suddenly hits the end of the leash. Use a short leash and soften the impact to prevent injury to the neck. It’s another reason why I like the Newtrix design better.) I like using a clicker because it is a much clearer form of communication. It means only one thing and the click sound is like nothing else. Black and white! This training takes a lot of discipline on the part of the human because the slightest inconsistency will impede progress. If pulling works occasionally, the dog becomes a gambler because the payoff is huge!
I highly recommend having someone take a video of you walking your dog so you can observe how you might be reinforcing pulling. Even extending your arm slightly after you stop walking so your dog can stretch his neck forward an inch can be enough to keep the pulling habit strong.