When I was road working a pair of my Malamutes (that is me on a bike and and them gaiting next to me on a coupler) we were attacked by a German Shepard. As my guys were coupled, that leaves them at a distinct disadvantage to defend themselves.
One of my girls sustained a gash to her hindquarters. I was so furious that I nearly took apart the shepard. I do not let my dogs run loose and expect the same from other dog owners. I also used to own an obedience school so know how to break up a dog fight.
I called the police and as this was starting to become common, my dogs being attacked by loose ones, I asked them what I could do.
The officer told me to get mace (the kind that streams). He said it would stop the attacking dog cold. BOY was he right! The next time it happened (only one week later). I spayed it in front of the dog (it shot out about 8 or ten feet away from me). With their sensistive noses, that dog looked like he hit a brick wall and took off running the opposite direction and I never touched him with it (although I legally could).
Even for walks, now, I NEVER leave without my mace. Since I got it, I've had to use it a number of times but neither me or my dogs have ever been injured again and I have never needed to actually hit the attacking dog with the stream.
I hope that this helps someone else.