I've had a lot of trouble with pit bulls as my neighbor breeds them. He's a very irresponsible pet owner. Key spray pepper spray works fine but takes a few seconds for it to sink into the dogs head what's going on. Then I really believe it becomes a seriously traumatic emotional event for them. Once it has sunk in the dogs I have sprayed have kept there distance from me after the fact and years later even when I enter their yard. So I believe pepper spray has quite a profound effect on dogs.
I also own well behaved/trained dogs that have got into fights with roaming unruly neighborhood dogs. I have healed bite marks on my arms and legs and I've killed a dog with a kitchen knife breaking up a fight as a matter of court record(a very satisfying suit/counter suit). If a good size dog wants to get a hold of you it will. My thinking is to give them your left forearm (that you've wrapped with a shirt if you have time) and do one of three things..... take a knife to their throat, keys to an eye or grab the skin just above and between the eyes pulling and twisting it.
The area above/between a dog's eyes very sensitive and working it should cause the dog to release you, your dog or your loved one. Just watch out for the nip at your hand as the dog releases, soon as he drops pressure from the hold pull of push him away to avoid it. This is hands down the best way to break up a serious dog fight without harming the dogs. Then use pepper spray on the bad dog to keep him off your dog or in a pinch use your feet or a blunt instrument to keep him off. One time I used pepper spray to break up a fight when they were locked and it made the dogs fight harder. Spraying both dogs was unavoidable while they were locked. I then had to use the above method and in the process became very intimate with the effects of pepper spray.
This stuff has happened over the years and I have little problem with the past few years. I have standing orders to shoot those dogs when they come on or property from my wife. I believe it's the fear of pepper spray that has settled everything down. Even new litters of puppies pick up on the fear from the adults and never come near us or cross the fence line. I'm a believer.