dirt-angler, let me save you some time: If you think that prohibitions about "digging" will preclude you from hunting a park or school lawn, then give up detecting at those places right now. Don't even bother asking "can I?", as no one can authorize you to break the law. Yup that forbid "alterations" or "defacement" or "digging" or "damage" or "vandalism" exist in ALL public places. I mean, duh, did you really think you were going to walk into city hall or school district office somewhere, and ask:
"Hi. Can I please alter, deface, damage, vandalize, dig, and destroy the park (or school) for my own personal pleasure and enjoyment?".
I assure you that clauses/verbage that disallow such actions exist everywhere. I mean, did you really think any place "allows" destruction and defacement?
Thus no, I do not equate my hobby with such terms. To do so ....... to make the automatic equivalence that md'ing = destruction and damage, is to give it up now. Stick to private property or beaches.
You have to recognize that the mental picture you are portraying with your "dig holes" portrayal, is the end result of ...... holes! Thus if you and I leave no holes, then nothing has been destroyED, defacED, alterED, and so forth. What could be more in keeping with the code of ethics than that??
Sure there's the temporary evil process of extraction, and sure someone can come up and debate the semantics of this interpretation. Avoid such persons, and go at low traffic times. If it still bothers you that you can not alter, deface, and vandalize places (if that's the laws you really feel apply to this), then ...... I suggest you've chosen the wrong hobby. Or you'll have to be content to look only for items on top of the ground.