reply
I prefer to get permission, Texas still has the law on the books that you can be shot for trespassing, ......
Trespassing in a park? How do you figure? Why would you be guilty of trespassing by being in a park? People in parks are not "trespassing". Perhaps by metal detecting you might run afoul of something
else ("alterations" or "defacement" and so forth), but no, not "trespassing".
As for your situation of finding various answers depending on whom you ask in city hall, this is not un-common. Odds are, there really is no rule *specifically* saying "no metal detecting" in Austin parks. So depending on what desk-bound clerk you ask, and their mood that day, and how they envision your question, and how you phrase it, will dictate their answer. For example: maybe one person thinks you'll harm earthworms, or leave craters. So they say "no" (mind you, that person probably perhaps would never have noticed, nor have ever given the matter thought before). While the next person might say "I don't see why not, go have a ball" (because they are in a good mood, and envision that you'll leave no traces, etc...).
So if you ask me, I do NOT leave it up to the arbitrary whims of desk-bound clerks, to go begging them to tell me an arbitrary "no". I look things up for myself (city websites usually have the charter and laws and codes of each city). If I see nothing specifically prohibiting detecting, then I see no more need to "ask permission", than I would to ask permission to fly a frisbee. If it's not dis-allowed, then it's not disallowed.
As for your followup episode of being accosted (even though you'd gotten at least one "yes" at city hall), this also is not uncommon. In fact, some have even gone so far as to have their permission in writing from some city hall person. Yet once out in the field, they STILL got flack from some cop or gardener! The md'r proudly whips out his permission to show the busy-body. The cop or gardener merely gets on his cell phone, calls down to city hall and says "well I don't like it, he's tearing the place up" (even though that's not true), and guess what happens to your "permission"?
So the best bet is to be a little discreet, and avoid such busy-bodies. If it's park maintenance day at one particular park, go hunt somewhere else that day. If you see busy-bodies studying you, don't be in the middle of a deep retrieval. I mean, it's gotten to where I simply hunt parks only after 5pm, or even at nights, JUST to avoid someone who might make connotations. Out of sight is out of mind. Just like nose-picking: sometimes you just got to be a little discreet. But sure: if you ask someone, "can I pick my nose?" of course they're going to say "no".