Its not really a solution but I know of one case where the interlopers were flying close at hand and were asked nicely to co-operate. A few choose not to and as a result a fairly expensive model at the club in question was destroyed. The modeler who lost the aircraft drove to the offending field and parked his vehicle on top of all the models there. He claimed it was no different than the disregard for his aircraft. I do not endorse or recommend confrontation but I can see it happening very easily.

Dennis