dusty-wallen, it depends on which level of laws you are wondering about. Ie.: what type land? Because think of it: there is multiple levels of ownership/oversight: Federal owned, state owned, county owned, city owned, and private owned. So which one are you asking about? And even within each one, there might be sub-layers of usages, codes, and rules.
For example: You know how there is "road right of ways" for state roads, and county roads, etc... where the road's asphalt edge might end at such & such point, but the "right of way" extends much further off into the distance out into the country. So let's say, for example, that you researched out that fruit-stands used to set up shop at a particular intersection, of what is now a state-road. So you decide to hunt the vacant corner of such an intersection, where the right-of-way extends off into the distance for aways.. Odds are, no one cares, even though that is state owned. Because perhaps there's pedestrian paths there currently, etc.... But you can see that this is quite a bit different that a state-owned sacred historically preserved monument park preserve (where no one would argue that we should be allowed to poke around and disturb). So using that example, you can see that whereas state PARKS might have one standard, it doesn't logically follow that all state land (under other state sub-categories of managment) would be held to the same standards or codes or laws. Same for city lands: whereas the rules may be "park closes at sunset", yet city streets (also city owned) you are allowed to be walking/standing "after sunset". So you see, rules differ even within each governmental entity, depending on where/what.
To answer your question, you want to look up the rules for yourself always. Because mfitz70 is right: All too often if you ask a desk-bound clerk, you might get a "no", simply because they choose the easy answer, or simply because they morph something else silly to apply to your question (when there might be no rule that specifically says "no metal detectors".)
All laws, codes, regulations, rules, etc.... from governmental levels, have to be available for public viewing, somewhere (lest how else is the public supposed to know if they're within the bounds of the law?) So for example, at city levels, it is usually made available down at city hall, in binder form, on the front desk, where you can read the city charter, etc..... And most cities (and counties, and state, etc...) are now on-line on the web. So you can simply go to their website, and it's there in the menu somewhere. Some, for example, are now subscribing to this service:
State Listing - Municipal Code Corporation
When looking through such resources, remember, you are not looking for laws which "allow" you to metal detect, but rather, you are checking to see if there's any prohibitions. If it is silent on the subject, well then presto, I guess it must not be dis-allowed then, right? And I'll save you some time, and tell you that almost always, at city and county levels, there is never anything about metal detectors/detecting. Perhaps in a few larger cities, there might be something, or a permit, but it is very rare, across the entire USA. And no, I do not consider verbage about "defacement" and "alterations" to apply to metal detecting. Because all such things implicitly apply to the end result. If you leave no trace of your presence, then by logical conclusion, you have not defac
ed or alter
ed anything.
