Patrick,
Never been hasseled by any authorities in the 3-1/2 years of renewing my hobby. In fact, most of the school security cars either honk or the guards wave at me. Guess they consider me extra security. The police only came over to see if I found anything good. Just don't use a shovel. If you haven't got one, get a Predator digging tool of something similar. It's less intimidating and makes a smaller hole. Try not to dig during major sports events. You should have no problems in most places. However, I have heard that Bay Shore schools chase MDers.
Stew