| Yea there is. I can start fiddling with my brand spanking new | synthesized transmitter until I "accidently" find your | frequency. One of the most impressive sights I have seen in the | hobby is that of how foam explodes into a white cloud on impact.
... but that's not nearly as impressive as the sight of a fully built up, giant scale plane disintegrating as it smacks into concrete (or a car or building) at 100 mph.
And if you think that's a valid solution to the problem of a park flier flying nearby, you're an asshole. And if you actually do it, you're a criminal, and if I were to see you doing it, I'll treat you as such, even if you were a member of my club -- meaning I'd tell the victim and club management, tell the police if he wants to call them, testify in court, etc.
And even if you are a bonafide asshole, you don't want to play this game. The club has so much more to lose than a lone park flier -- not only are your planes generally much more fragile, larger, faster and more expensive, but your site itself would be in serious jeopardy if it were ever found that a club member ever intentionally interfered with somebody else's plane and caused damage or especially injury. Accidents are one thing -- but intentionally damaging somebody else's property (or causing injury) is criminal and would probably land you in jail and could get the club booted out if it could be proven.
Here in Austin, Texas, there's three AMA clubs nearby -- HCAM, ARCA and the ASF. I don't know much about ARCA, so I won't comment on them, but HCAM and ASF both have sites on public parks.
HCAM is very well established, and their site takes up about half of a city park, but has exclusive use of that section of the park. There's a paved runway, building, storage units, porta-potty and a locked gate. I believe we rent it from the city for some tiny figure -- $1/year or something. AMA is required, but membership is not, at least not for just a few flights.
ASF is a electric/glider club, and brand new. They have permission to fly at their park and a section set aside for them, but so far have not been allowed to make any improvements to the park whatsoever. For now, their site is just a field off to the side of the park with no gate or even a sign. AMA is required, IC engines are prohibited.
I don't know if ASF has exclusive rights to it's property, and so I don't know if they could refuse to let a park flier fly directly with them, even without AMA. Knowing how some of the people in that club are, if somebody tried and was stubborn about it, it would probably get ugly. Hopefully it won't ever happen.
But HCAM does have exclusive rights to it's site -- but not over the rest of the park, right next door. Austin does not prohibit R/C flying in it's parks, so there's nothing stopping a park flier from flying in that part of the park, or at the middle school a few hundred yards away. And it has happened, and will continue to happen.
When it has happened in the past, some members have flown off the handle and done I don't know what. And then it was brought up in the meeting where people were all saying `they can't do that!' ... at least until it was explained to them that the law says no such thing. They have as much legal right to fly there as we do at the AMA field. We could try and get the parks department to ban R/C flying in the parks except for our field, but it was decided (rightfully so) that that wasn't very fair, and would cause problems for other people, and that wouldn't actually solve the problem anyways, because there's lots of private property near there park where people could fly too.
Ultimately, it was suggested that if somebody notices a park flier, people should land and go over and talk to him, find out what frequency he's on, explain the problems, and suggest that he either not fly there, or at least come over and work out frequency sharing before he turns his transmitter on. As far as I know, most people have been agreeable to this when approached like this, and there have been no incidents. Most of the time the park fliers are on 27 mHz so it's much less of an issue, but when they were on 72 mHz, people just put in a note in the frequency board saying that there was a park flier over there, and it works fine.
The very best solution would be to invite them to fly with us at the field rather than near the field, but since the regulations absolutely require AMA membership, that's really not an option most of the time. Which is really too bad -- but the AMA doesn't really have much to offer your casual park flier, so there's little incentive for them to join.