I agree on both accounts. You might even look at getting something like an air horn. They're pretty good at breaking up fights.
Just wanted to say how sorry I am that this happened to you, your friend, and your dog. This pit needed to be put down, end of story. There is no solution for his issues, it seems from his history. it's best that he's been put down, things are safer now.
Sorry to say, but if breaking a chair over this pit and kicking him in the face didn't distract him from trying to attack her dog, a fog horn ain't gonna do it either. Dogs determined to fight will do so with or without human interference. As you can see, she and her friend already got bitten. Imagine this angry dog suddenly being scared by a loud noise coming from a human and then turning his attention fully on her. Not good either.
For most dog fights, pulling each dog apart from each other by grabbing the tails (NOT BY THE NECK OR COLLAR, YOU WILL GET BITTEN!)will do. However, when you have a dog locked on to the other that won't let go, that won't work either. Like I said, a dog determined to injure the other one is going to do so with or without a human's interference. It's scary stuff right there, a dog attack. I don't recommend a gun, too many things could happen with that, like they said. I'm not gonna tell you what you should or shouldn't have done cause I wasn't there so I don't know. My dogs protect me, and I'll do anything to protect them though.