I agree with Miss Prissy- This society is far too lawsuit happy to take any chances. Post no trespassing signs and warning signs. After that... it's their fault (hopefully). Booooo to trespassers.
Might want to try a "WARNING: BULL PASTURE" sign on the fence. Or a nice "trespassers will be shot" sign should make your point. It is rude that people think they can just go where they want in an open space.