Hey there silver-1, this is the "bee in my bonnet" topic. Doh. And yes : You have discovered the "aha moment".
Basically it's this: "Sometimes: No one cares UNTIL you ask"
Ok. And why isn't "the right thing" to do: To look up potential laws/rules for yourself ?
If you find nothing in the muni code or park rules that says : "No metal detecting", then presto: It's not prohibited. Right ? Why wouldn't that be the "right thing" to do , to answer this question ?
The trouble with asking desk-bound pencil pushers is multi-fold: The mere fact that someone is standing there, at their desk (or email or phone call) asking "can I do such & such" : Merely implies that something is askew. Eg.: Potentially harmful, illegal, damaging, etc.... Otherwise : Why would you be asking ? No one asks if they can do innocuous / benign things. Right ? Eg.: fly frisbees, skip stones on the pond, etc.... Therefore, the moment someone is standing there asking "Can I?", that simply infers something is risky or harmful or whatever . And then guess what ? That simply steers their answer
Then you end up getting a "safe answer" to your "pressing question"
I have seen this over and over and over at places where ... . quite frankly ... it was never a problem prior to that
And worse yet : Sometimes a law or rule or policy is "born". Eg.: guess what that same person (who passed out the 'no') will think, the next time he passes the court-house lawn, and sees an md'r ? He'll think "Aha ! there's one of *them*". And start booting others (that... previously ...he'd have never have noticed or paid-mind-to).
Not saying that md'ing doesn't have connotations in nice-manicured turf. Fine then, go at night, or early or late on Sundays, etc... If you want to call that "sneaking around" ? Fine then: Sneak around. It's a little like nose-picking: You can knock yourself out trying to get every-last-person on earth to approve of you. Or ... you can just practice a little discretion in timing.