ORIGINAL: Matt Smith
I know it's not enforecable and it may not help you much, but the other flyer you mentioned shouldn't be flying from his backyard less than three miles from an active r/c field in the first place! The onus is on him to comply with the AMA guidelines. If this guy continues to operate this way, there is the possibility of him causing a lot more problems in the future. What if he buys a new radio on a different channel? Perhaps I'm missing something, but why does the club not approach the individual about his frequency usage?
If he's not an AMA member, he's not obligated to follow AMA guidelines. If a crash occurred and you (or any injured party) could prove that he caused it; someone might get money out of him.