ORIGINAL: sfsjkid
Part of me wants to say gather as many transmitters as possible and turn them on. But that wouldn't be responsible.
I was wondering, is the land private property or managed by some goverment organization? They could be considered trespassers, using the land for purposes not allowed or hazard to motorists if near the road. Another weird suggestion comes from the fact that an endangered species of owl calls uses our field as home. The animal perservationalists visit sometimes and would have a fit if they knew we were harming them.
Our club has a similar situation but fortunately with another club, and the spacing fortunately is 3.2km away and doesn't cause problems. The AMA however wants us to do testing since the regs call for 4.8km between clubs.
Hope you get the problem solved!
The AMA has these documents but don't help if the other party is unco-operative.
http://www.modelaircraft.org/PDF-files/535-G.pdf
http://www.modelaircraft.org/PDF-files/535-F.pdf
Get a frequency scanner so you would know what transmitters to turn on.
Really there is nothing you can do. This is one of the reasons we need spread spectrum. Soon there will be more and more toy grade equipment on 72 MHZ. I could be a problem for many of us.
Driving over their airplanes would get you a visit to court.