wow ace, that's just crazy. But oddly, I can see the public officials point-of-view, when they say:
"Even if it is not buried and it is just placed somewhere it becomes public domain."
If you wanted to get "down-right-technical", this probably is true. I mean, there has ALWAYS been rules and laws that forbid "harvesting" "taking" "collecting" "removing", and so forth, RIGHT? Now the OBVIOUS intention of such rules is so that no numbskull thinks he can go taking the trees, or harvesting the turf in the park for use in his own garden, or taking the swing-sets, or sawing down limbs of trees for firewood at the down-town park, and so forth. Right? I mean, duh, the laws saying such things pre-date metal detectors afterall.
And why can a public entity get away with such verbage, because as that link says: technically, park features belong to the govt., NOT just any yahoo who comes up and starts taking things. You know the old addage that if a beach is pretty because of a certain peculiar pretty stones found there ........ that if "everyone came up and took just one rock home, then very soon, the beach would no longer be "pretty" ".
So technically speaking, such verbage can apply even down to singular coins, rings, pulltabs, etc... Heck they can apply to arrest your 4 yr. old daughter if she picks up a pretty sea-shell off the beach, if you asked enough lawyers "can I?".
And even if you or I try to counter-argue that the object doesn't necessarily belong the govt., but instead belongs to the person who lost it (the rolex, the diamond ring, or whatever), then THAT only opens up ANOTHER can of worms, that it's STILL not "yours", no matter how you look at it.
So if any of us is bothered by such "connect-the-dots" reality, and if anyone of us thinks he can abide by all laws while partaking of this hobby, you are sorely mistaken. Anytime you go out, there's probably 5 or 6 laws you've broken, even at the most mundane innocuous sandbox.
The REALITY is though, that no one cares when you and I ply the beach and keep the trinkets and coins we find, right? But sure, if you asked enough archies, lawyers, and desk-bound bureaucrats "can I keep this for my own fun and enjoyment?", what do you THINK they will be obliged to say?
Thus I put little stock in legal fears proposed in stories like this. If the day comes that things like this make me have fear or pause, is the day you and I might as well give it up now, and choose another hobby. Because I assure you: that article is probably right, that anything in the park, is a part of the park, NOT for you to enrich yourself "at the public's expense". I say that in jest, because I FULLY intend to not stop, and keep detecting. Why? Because no one cares except a few ivory tower archies interviewed for some d*mb story, who will never see me, nor care, unless I ask them "can I ?"