When I was a kid, we had a neighbor who had somehow wrapped some wire around the power lines enough times to siphon off an interesting amount of power. I never saw the wire myself, so it might not have actually happened. But people certainly talked about doing it way back when.

We had a neighbor that put loops of wire under a 600kV line and got enough power to run a water pump for cows. The square law makes that kind of thing pretty low-return.