Can't your parents get on board and have him keep his dog contained since he is their guest? Technically if it is their property and say a big dog fight broke out and either his dog got injured/killed or he got hurt trying to break up a fight...couldn't he technically sue them? (I'm just thinking that might get your parent's attention...mentioning money usually gets people to at least give what you are saying due consideration.) And no matter how good a friend this person may be...you never know who is lawsuit crazy even if they don't have a legitmate reason to be. Personally I think your parents are assuming allot of risk...