Hunter GT, you are doing good to have always avoided having the person give a whimsical "no" (as if you'd just asked their permission or something). And this is exactly why many folks on md'ing forums, point out that it's important (as you probably already do) to phrase it:
"Are there any law/rules in city code that deal with , or prohibit, the use of metal detectors?"
Because by phrasing it that way, you're putting the burden on them to CITE any such law or rule, if one existed. And so far, you seem to be doing good at keeping people on-point. And you said that if they changed subject, and started give some sort of whimsical opinion you would indeed re-direct them to the specific question. You say:
"Never once have they given me there preference or opinion...and I would absolutely ask for the law/code if they did."
So with that in mind, here's a true story that occurred in that situation. A man asked a city clerk (yes, I know, his first mistake, but the principle *could* happen with an LEO). The clerk said "no you can't". The man re-directed the gal back to his question by saying "where is that written? ". The lady looked to & fro through her rule books, and had to concede there was nothing that specific. So the man left, and that was that.
But I guess the lady must've had images of yahoos with shovels in the park. Because GUESS WHAT WAS ON THE NEXT WEEK'S CITY COUNSEL AGENDA? : The proposal to make a rule forbidding detectors in that city's parks. Hmmm, I wonder what caused them to all of the sudden think "let's invent a rule!". Obviously it was the persons in there with the un-mistakable challenge attitude of "be prepared to show me chapter and verse, if you plan to say no".
Anyhow, in the old days, it was probably true that city codes/laws would have been hard to find. You'd have had to go into city halls, legal library, etc... asking for a dusty binder that's kept somewhere at city hall, blah blah. But nowadays, it seems that nearly all cities (except perhaps very small podunk towns) have their laws/rules/charters/codes on their city websites. And if they didn't, you could always still ask the live person: "where can I find the public codes available for public viewing?". If they change the subject and say "what is it that you wanted to know?" I'd repeat the question "where can I view all public laws, permits available, codes, etc...". It HAS to be somewhere for public viewing.