There have been instances of other FM pirates doing this. They would record a show in their home studio and then drive a vehicle carrying a powerful transmitter to a hill top far above large cities and then run their show. It can be quite hard to track down a signal like this since you have the ability to drive away if anyone suspicious comes near you. You could get friends to keep a look out also and use 2 way radio to keep in contact. Unless your running a few hundred or more watts of power and broadcasting stuff that pisses people off I don't see really going to this length of security to be honest.
If you're really that worried with only a few watts then just setup the transmitter at a remote spot and send your audio to it using an internet connection, or use a wireless Stereo Transmitter Link but make sure to monitor your signal so that if some bozo comes and unplugs your transmitter you know to kill the STL connection right away so they can't track the UHF signal back to your studio. The internet idea works better for security then using STLs though since it's very hard to track down to the studio base. The good thing with this method is you can keep your operation running as long as you want until someone unplugs your transmitter, but you do risk someone stealing it like the FCC.
I have a few hlly transmitters. The best one is the tx 99. It needs A high quality low pass filter, Then everything seems to be fine. Never scoped it yet . I will soon .
yep, depends where you are. im in a major city that is overcrowded with dirty rap stations that the feds wont touch. the "urban" fm stations are a great shield. the agents come and do their job, you flip the switch and make them happy and they are on their way.