Depends on the nature of the fight. I've broken up fights that way that were mostly noise. When my family was dealing with warring females, a vet behaviourist said get two people to grab the back legs of each dog and both should slowly walk backwards. I've seen a similar version using leashes as per JoeK's description recommended by a Pyrenean breeder. Apparently in the military they lift the dog's back legs up like with the Greyhounds. I've heard sticking a finger/hose up the dog's backside makes them let go. :p
Never had to lift my rescue greyhounds back legs they don't know how to fight LOL.Still get the same reaction at the dog park from some hysterical owners because my gentle giants wear muzzles(sigh so frustrating)and they're never off lead (unfenced)Have seen aggressive dogs at the park,both large and small not discriminating,yet my two still get the glare!Finger up the butt does work friend had to do it once to stop a large dog killing a small.