Most of the stuff is not just lying on the surface; it's partly buried or covered. I've gone to cut down tree branches and found sections of barbed wire 6 feet off the ground because it rose as the tree grew and snapped off when it was pulled too taut.

Not to mention that the ground isn't flat like a nice suburban lawn. There are creeks to cross, rocks (that we are constantly removing as water exposes them), fallen dead trees, tree stumps, wild grape vines, channels dug into the ground by rain. Obstacles galore!

You won't find many people more in favor of automation than me, but even I know when to stop.