I've stayed out of this thread completely until now because I beleive your analogy is totally off the mark. I respect all property rights, both on streams and off. The idea that you being in my house, in my easy chair, and drinking MY BEER, is similar to me walking onto your property while in a stream is utterly rediculous.
1) I have a lock on my front door.
2) I have obvious property lines.
3) I have a "No Trespass" sign on a corner post right beside my driveway entrance.
If you don't want the wayward fisherman crossing your property line you should invest in a little signage or at least some purple paint. I, like most respectable fishermen, would recognize and respect that and turn around. If a property owner who knows these things might happen and doesn't do the necessary things to avert trespass, he should at least give the individual the benefit of the doubt and inform him of the property line and ask him to leave. There's no need to get nasty like a lot of these people do.