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Looking for the least restrictive state for MDing.
Do you mean at the state land administered level? Because of course, entities lands within an individual state (county and city lands) might be totally relaxed, and no one cares, etc....
Have you consulted this list yet? :
Federation of Metal Detector & Archaeological Clubs Inc.
But even that needs a few footnotes:
a) it's only for state PARKS lands. And of course, there are other types of state administered lands that are not necessarily "park" land
b) often time beaches are treated differently than land parks. For example, that list says of CA that we are to inquire of each park, get permission, blah blah blah. But I can tell you for a fact that you can hunt state-of-CA administered beaches here till you're blue in the face, and no one cares. (so as you can see, it would be an UN-wise idea for anyone to go seeking clarification of that, RIGHT?

)
c) That list was gleaned decades ago (and altered at needed, I suppose), by a seemingly obvious method: Whomever starts a list like that simply sends off an inquiry to all 50 states head-park-dept headquarters ..... and
asked! Doh. Seems logical enough. I mean, who better to ask, than the states themselves afterall

But oddly, whenever the desk-bound bureaucrat way-back-when receives such an inquiry, what do you think the safe answer was going to be? A lot of them sent back odd replies tying in odd-ball stuff like cultural heritage verbage, etc... with dire sounding answers. But the odd thing was, that in a lot of those "dire sounding states" detecting in their state-level parks had simply gone on, as long as anyone could remember (and perhaps still does at some parks). And no one had ever had a problem before. So you had old-timers looking at a list like this, scratching their heads, saying to themselves "since when?" (see the self-fulfilling squeeky wheel psychology here?)
And even if someone could tell you that any particular state has "lax laws", it would only mean they didn't ask high enough up the chain of bureaucrats and archies in their state, with the right combination of buzzwords. Becuase if you ask long enough and hard enough, you can always find a "no", even at the most inncuous of sandboxes. And so, conversely, if someone thought their state was "not relaxed" and had "ominous laws" it might be that they're just too skittish, and reading archaic dusty minutia which, in the field, no one really cares about or enforces (unless you're being an absolute nuisance snooping around obvious historic monuments).