TH'r, ok, let's cut to the chase then: Are you aware that laws (or rules or codes or ordinances, or whatever someone wants to call them) are on the books in EVERY park across the entire USA ? So if that boiler plate word is to stop us, then ..... hmmmm, we're all in a big heap of trouble! But last I looked, there was no shortage of md'rs hunting parks.
Even if it didn't use the exact word "dig", it will still be there in some form or fashion. Eg.: "alter", "deface", etc.... Now these latter types of words are much easier for us to deal with. Because they inherently infer the end result. Eg.: alter versus alter
ED, etc... But yes, the evil word "dig" (a present tense verb) is not as easy to get around.
But just saying that that word, and a multitude of other concepts and words ("remove", "collect", "take", "annoy", etc...) that could, if you asked around enough, be applied to our hobby. So when you start down that path, then you might as well give up all public land everywhere