I just wanted to put in my 4 cents (I talk a lot so it's worth more than 2) in case anyone is interested or has had the same problems we have with a major puller on the leash.
I have tried both the Halti and the Gentle Leader and wanted to let you all know what I think of both of them.
Both are great tools to use to help with training a pulling dog not to pull. They both work in basically the same way - they use a gentle pressure on the muzzle when the dog starts to pull in order to turn the dog's head back towards you. The basic principal is: where the head goes, the dog will go, thereby making it virtually impossible for the dog to pull your arm off as you walk.
Kentucky would pull so hard on the leash before we started using these that she would be walking on only her hind legs.
Since we started using the Halti and the Gentle Leader walking has been a much more pleasant experience.
I recommend both of these if you have the same problem. Here are the differences.
1. Price: The Halti is about $5 to $10 cheaper than the Gentle Leader, but the Gentle Leader comes with a training guide and a training DVD (which I keep saying I need to watch, but haven't yet).
2. Ease of use: At first I thought the Gentle Leader was easier to get on the dog, because it is built more simply than the Halti. The Halti looks like a half-muzzle attached to a collar with the lead coming out the bottom. The Gentle Leader, on the other hand, is a similar collar with one other loop. However, I find the Halti sits more comfortably on the dog's nose than the Gentle Leader. If the GL is not attached exactly right, it tends to slip up too high and irritates the dog's eyes. Also, because the Halti's muzzle-portion is fixed and not another loop, it's easier to get on a jumpy, excited dog.
Overall, both of these tools have made walking with Kentucky a lot easier, but I prefer the Halti slightly more. Training to walk with a loose leash is the same with either one and you have to be prepared to look like a spaz or borderline narcoleptic. If your dog starts to pull as you walk, you stop, pull slightly on the leash to turn the dog's head back towards you, call to her and praise her when she returns to your side. We used treats to reward her for returning to the proper position (and to bribe her back) at first. Now, the walk is her reward. We still walk about 10 steps, stop, walk 15 steps, stop, walk, stop, walk, stop, walk, stop, but by the end of the walk she remembers what she's supposed to be doing and our leash arm is no longer 10 inches longer than our other arm.
I'm looking forward to hearing your experiences with these two tools!