hogman and nugget-hunter, I have no doubt that EVEN if any of us md'rs finds specific wording ALLOWING detecting, that someone else will have an experience (or something they heard second hand, blah blah blah) that contradicts this. I mean, it stands to reason: if you ask enough people ANYWHERE in this world "can I do something?" you will eventually find someone to tell you "no".
A buddy of mine, for instance, just the other day, helped himself to an old-town street demolition job here in CA, where some seateds had been found recently. It is not fenced or posted, but there is a few orange cones and ribbon around it though. The contractor/construction people themselves, had shrugged their shoulders and didn't care if he detected (just told him to come back after hours after they knocked off for the day). Well one night, when my friend was there plying his luck, a state worker came out of one of the offices along this street, and started telling my friend he had to go, "because of terrorist threat" (I guess she didn't know what his detector machine was?). And when my friend refused, saying it was a harmless metal detector, then she changed her tune and told him "this is private property". And again, my friend tried to tell her "no, this is a public street". And on and on the debate went (she was a nut-case, and her rationale was illogical).
Now why do I give this as an example? Because as you can see, NO MATTER HOW INNCOUOUS, there will sometimes be a kill-joy ranger, bureaucrat, busy-body, etc... to try to say you can do it. And all too often, what happens on these forums, is someone has one of those odd-encounters, posts it (going so far as to do what hogman has done, and say "you can't hunt in such & such place".) And then everyone else shudders in fear after reading this, and simply believes it. When all too often, it's really just isolated incidents, and odds are, no one really cares (barring if you were a nuisance in some other way, or ran into a rare barney-fife-type).
So for pete's sake, if the occasional busy body bothers you (if you're skittish) then by all means, stick to sandboxes with glaring neon signs that say "metal detecting allowed here". Because otherwise, you've chosen the wrong hobby. Unfortunately, we're in an odd hobby that draws the stares of the curious (ie.: "oooh, what's the man with the geiger-counter thingy doing over there?" etc...). And there's no way you're going to please everyone, and have everyone sign off on your fun. So why can't we all just practice a little discretion, and simply avoid the few busy bodies that exist out there?
Even if it were true, in texas, that they make a law more strict than it really is, I have to ask myself: did any of you plan on parading around in front of archie's houses, kiosks, wearing neon yellow? Because odds are, the rank and file could care less, so long as you're not snooping around obvious historic landmarks, and don't look out of place, etc...