I will say that where I camp, I rarely have a problem with dogs or their owners. Most follow the rules and, if they do let their dog off leash, they are aware of their surroundings and will have the dog under control before my dogs notice them.
I have found that how I approach people changes their reaction. If a dog is loose or in my site on an extended leash, I simply say "hey, could you get your dog? My dog's been attacked several times and has issues with strange dogs approaching him". By blaming my dog, the owner doesn't feel attacked and will usually call in their dog and not bother us again.