Ugh, I was just catching up on this thread and read all the pit bull stuff. I am an Animal Control Officer up here in Wisconsin and boy does that breed cause a lot of problems. Not much will stop them, even bullets aren't always effective unless you hit them just right. There are certain sprays you can buy, but those don't always work either. The only good thing about pepper spray is that if you spray the dog and it returns home to the owner, the owner might have a good time dealing with getting pepper spray on themselves or inhaling it after handling their dog. I hope your neighbor really does get rid of the dog, that's really the only solution, especially since it will want to come back over to your place after all the "fun" it has there.
I'm sorry Animal Control wasn't very supportive. I am always understanding when someone's chickens get attacked, I know how it feels! A lot of times people don't understand how much we care about chickens. They aren't just egg or meat producers, they are our pets!