I imagine with 100 watts in a tall tree over flat land you should be able to get at least a 25 mile radius.

I wonder what tools the FCC uses to find transmitters? I'm sure they can do triangulation with the signal strength and narrow it down to a certain area. But if someone sticks it way up in a tree in the middle of a swamp running 24/7 on one frequency, could they find it. Maybe infrared to look for the heat of the amplifier? Even so, I think you could get around that.

But I guess sound quality would be another problem....