As the owner of a rather aggressive dog (to other dogs, well, basically anything that wasn't a person really) that I had to put down, jeezus, a year and a half ago now, if you find yourself in the position of the previous poster who had to break up the dog fight here's what you do. Grab a fizzy drink (beer, coke, lemonade, west coast cooler [after all, it was a nice day at the park]) , shake the shit out of it and spray the foam up the nose of the offending dog. It coughs and splutters and you get it off the victim dog.
No need to beat off (I think I've got the wording right) the offending dog. That's how I used to justify walking the dog with a few beers in pocket and in hand, just incase. And why I was no doubt known as "the drunk prick with the pig dog" everywhere I lived.