It is not un-common, in this hobby, to get all sorts of claims, pointing to a wide variety of supposed rules that anyone speaking to you, may try to morph to apply to you. Because let's face it: we're in an odd-ball hobby, which draws the stares of the curious to the "man with the geiger-counter thingy".
And then of course, if they see you with a probe or leshe, we all know what some people's knee-jerk reactions is
So it's practically inescapable that there will sometimes be busy-bodies objecting. And if you were to ask them "but where is that written?" I'm sure they can come up with a myriad of things they think apply. Others would include "don't disturb the vegetation" (or earthworms, or birds with the frequencies your emitting, or whatever). Another is "prohibitions against collecting", or how about "you have to call the utility co. before you dig". And in each case, the md'r can try to argue that whatever lame thing they are saying, doesn't apply, but guess who will loose that debate?
And if you (or the person in your example) won the debate, and showed that busy-body that this rule didn't extend down to city lands, guess what would happen? That person would merely try the "damage" clauses.
Heck, they don't even need a rule to begin with!! Merely being a public servant, they can literally just say "because I said so!". I had this debate upon being booted from a city location, where I happened to know for a fact that there was no prohibitions. The worker would only say "because it's not allowed". When I asked "where is that written?", he said "if you're gonna be difficult about this, I'll call the cops". Of course, I left, but I proceeded to research the matter, feeling that I had been un-justly booted. I mean, doesn't it need to be "written" somewhere? Not just morphing something nilly-willy to apply to you, that is totally arbitrary? So I contacted a lawyer friend, who said that public servants (cops, gardeners, rangers, etc...) can indeed do exactly what he did. The reason is, that public servants are given a wide degree of latitude to interpret "AS CONDITIONS MERIT", to apply to a myriad of circumstances. Because otherwise, people would be arguing semantics with cops all the time. For example: Let's say there is an anti-nudity law in your park. And let's say you went there wearing one sock. If a cop tries to ticket you for nudity, you could try to tell the officer, "but officer, I wasn't technically nude. I was wearing a sock". Or how about a sign that says "no dog walking". If your dog is an amputee, with only 3 legs, you could object and tell the officer "but officer, he only has 3 legs. Therefore he wasn't technically walking, he was 'hopping'". And so forth, and so on. So if these matters ever got to courts, judges will usually always side on the behalf of the enforcer, lest there be utter chaos in the field of enforcement.
So applying this to your situation, there may somehow be some legal argument that this state-level rule, applies down the line to cities and counties (I highly doubt it), but *in reality*, I bet your friend's situation was unique, and probably an anomoly. Far too often people get told "you can't do that", and they don't question it, and just run for fear of authority.
For example: Decades ago, when I first got into this hobby, the buddy that got me into it, told me one day, that "detecting in such & such's city's parks and schools is illegal, and you can be busted, ticketed, confiscations, etc..." I took the warning to heart (afterall, what did I know? I was just a beginner, and this was the experienced person). Years later, about 1980, another un-related hunter friend started finding silver in a particular park in this town (as this was the genesis of the deeper seeking motion VLF days). Word spread amongst the hobbyists here, and soon, several of us joined him and enjoyed hunting this park in that city. But in the back of my mind, I couldn't help but think "I thought detecting in this town's parks/schools was illegal?". But no one ever said anything to us (even in full view of traffic, workers, etc... who paid us no mind), so I just sort of dismissed it. Later on though, I was to run into that original buddy, so I asked him "who told you that detecting in that city was illegal years ago?". He related the following rationale: His brother, in the early 1970s, had gone to a school there to detect in that town. A janitor came out and told him "you can't do that". To which the md'r says "Oh, I'm sorry. How about the school down the street. Can I detect there?" The janitor says "no, not there either". The md'r says "hmm, how about the park downtown?" The janitor, growing frustrated, says "you can't detect on city property in this city. It's against the law". The dejected md'r left, and promptly told his brother, who promptly passed the word on to others (afterall, you can't be too safe, right? You can't argue with a city employee who certainly knows the law, right?).
But think of it: perhaps the md'r was there during school hours? Or perhaps it was just a single janitor, having a bad day, who thought he might leave holes? etc.. And rather than debate law, or whether or not there was actually holes, it's easier just to say "that's illegal", and point to anything the person thinks applies.
So sometimes it's just best to avoid busy-bodies, and go at off-times. For example, if you arrive at a park or school, and see that that's the on-day for park worker maintenance (lawn mowing, etc...) well choose another park for that day. In fact, it's gotten to where I mostly hunt parks and/or schools at off-hours: after 5pm, or weekends early, etc.... *just* to avoid busy-bodies.
Lastly, I have no doubt that if you (or your md'ing friend who got booted) were to ask the WV state's archaeologist: "does this law extend down to city and county level public lands?" that of course they'd say "yes". But that's sort of like asking a PETA activists (animal rights wackos): "can I leave my pet bunny in the car for a minute while I run into the 7-11 store?" They'd scream "NOOOHHH!! That's animal cruelty! You can be arrested, ticketed, fined, jailed, etc....!" So too is asking an archie "can I metal detect?" going to be met with immediate "no's", no matter if the answer is really, legally, no or not.
Because if it were true that state laws trump cities and counties, why doesn't federal laws trump state laws too? (afterall, the 50 states are a *part* of the larger federal entity, right?) It just doesn't make sense.
