David, your example using your front yard isn't comparable. Your front yard is obviously private property. Most land immediately adjacent to public highways in this country is government owned, which means they are accessible to anyone. That's not to suggest that anyone can do anything they want to on that property, but entering it is not trespassing. Large parcels of private property adjacent to public highways are fenced off - a declaration of private ownership. No fences, or no signs declaring the property to be privately owned often means the property is government owned. Since this particular property wasn't clearly marked as private, either by enclosed fencing or regularly spaced signage, trespass violations would be just about impossible to prosecute. Now that the property owner has erected signage indicating the property is indeed private, forget about digging...just walking on it could have you trying to defending yourself in a courtroom.