In PA, I think there at least used to be some law that favored actual practice over property lines, IIRC.

Something like..if you let a family cross your property as a regular practice for some amount of time, you couldn't then just cut off that privilege.

I could be way wrong on that though.

Excerpt from Robert Crais' "The Monkey's Raincoat:"
"She took another microscopic bite of her sandwich, then pushed it away. Maybe she absorbed nutrients from her surroundings."