I have run into this situation several times in the last few years and I just politely ask them if they really feel they need to be that close. Most of the time they just move away, but on the one occasion that they insisted on staying there I just paddled away and then went to a couple other boats near by and told them that the guy over by that log was really getting them and that maybe they should try over there. The crazy thing is, it actually worked and two other boats pulled up anchor and moved right in on top of the guys. Maybe not the nicest thing of me to do, and I am sure it will probably come back to haunt me one day, but at the moment it seemed like the thing to do.