The trick is to damage one of them badly enough (albeit non-permanently) that nobody else wants to try. I generally found that picking somebody clean off the floor by the throat and holding them in midair until the look came into their eyes where I knew they thought they were going to die was a good option. Doesn't give them much except a day or two of a sore throat in terms of physical damage but you only have to do it once every two or three years to be marked "not an easy target".