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Grumpsrb, let me save you some time (you owe me a 12-pack now): There's no need to "check". Yup. Every single city park or school yard you come to DOES have rules against "digging". There, now what are you going to do with all that time I just saved you ?
It's there in all cities, county, state, etc... public lands. Might not use the exact word "dig", but at least something similar like "deface", "alter", "excavate", "remove", and so forth.
So does this mean you're going to stick to private property from here on out, and cease detecting all public land? Probably not, because you'll say a person can "get permission" despite those rules/laws, right?
Ok then: try this: see if you can "get permission" to text and drive. Afterall, you're a safe driver, and you'll be careful, right?
What will they say? They'll say "no", of course. Why? :
Because they can't grant you permission to break the law. Then why is it that they CAN (sometimes) say "sure go ahead and dig, as long as you're careful and leave no trace" ? What makes texting laws, versus digging law different?
[that's a rhetorical question. I already know the answer. But am letting it sink in and shed light on this topic ]