Are parks where digging is not allowed worth it?
Are using probes allowed? If so, do you have much success?
Liquid metal, exactly what is the wording of the law/rules that you speak of ? Does it specifically say no "digging" ? Or is it something along the lines of "alter" or "deface" type verbiage ?
But it's all a moot point. Let me save you some time. There is not a park in the ENTIRE USA that doesn't have something along these lines ("vandalize" or whatever). And ANYBODY can say that our actions violate that. Do you really think you're going to win that battle of semantics ?
Thus if you think such things automatically mean "no detecting", then you might as well stay out of every park in the USA. But ... oddly .... a quick look at any finds-forum posts, shows NO SHORTAGE of guys md'ing parks. How can that be ? Are they all lawless miscreants ?
Here's what you have to realize: All such verbiage INHERENTLY applies to the end result. Eg.: if you've left no trace of your presence, then logically you haven't alterED or defacED anything, now have you ? And I would say the same for dig versus dug too. Does that mean every last busy-body will agree with that ? Of course not. Ok, pick lower traffic times and avoid such lookie-lous. You're simply not going to get red carpets rolled out for you.
And no amount of permission-asking solves this. I mean, gee, if you walk into any city hall and say "Hi, can I dig holes in the park?", guess what they're going to say. And to the extent you can debate the difference of "probe" vs "pop" vs "dig", guess what happens when some lookie-lou in the park doesn't like it ? You whip out your "permission", right ? The busy body gets on his cell phone, calls to city hall and says "but he's tearing the place up!" (which isn't true, of course). Then guess what happens to your permission ?
I would also point out that whatever answer you get , will vary depending on who you ask, how you ask it, their mood, what they envision, etc... FAR FROM "CUT AND DRIED" policy. Why subject yourself to that ? Don't become a victim of "no one cared TILL you asked". Just grow a set and go. Pick low traffic times. Kind of like nose-picking: Not illegal, and no one asks permission, yet you pick discreet times so as not to offend the squeemish.