Chris-play, OF COURSE there will always be prohibitions, in/on ANY public land, forbidding destruction, alteration, holes, digging, disturbance, vandalism, defacement, and all such wording. I mean,
what did you expect?

Did you think you were going to be able to walk into any city hall, in any city in the USA, and say "
Hi, can I please deface the park please?" and they tell you "
sure, have a ball!"
But think of it guys: All those words DISTINCTLY refer to the end result, do they not? So if you've left no trace of your presence, then by logical definition, you have not alter
ed, vandaliz
ed, or defac
ed anything, now have you? So do not make the automatic equivalence that md'ing = destruction, or you'll have lost the battle already. Because all places forbid such things. But since you know, and I know, that we will cover our spots and leave no trace, why isn't that good enough?
Sure there's the temporary evil process of extraction, that someone can debate our semantics of definitions on. You've got to be a little discreet, and avoid those type busy bodies. I wish the red carpet were rolled out for me too (with neon signs saying "detecting and defacement welcome here"), but it's simply not going to happen. You're simply not going to be able to waltz over beach blankets, and go right in front of landscapers, during archie conventions. I mean, this is a little like nose picking, you have to be a little discreet on your timing, for pete's sake.
If it really bothers someone that they can't find a place that "allows" destruction, digging, alteration, defacement, etc.... And you truly believe your hobby is defined in those terms, then I'm afraid you've chosen the wrong hobby. So please remember, those terms refer to the end result. And simply avoid persons to differ with this interpretation.