I was commenting on the remark of, always tell them no you didn't find anything. Yes the cops probably will let you go, BUT if they SEEN you metal detecting, SEEN you pick stuff up, then come up and ask, hey ya find anything and you say no, THEN they are going to be out to get you. No Lying is not a felony, but digging up 'artifacts' might very well be, and if you pissed the cop off by flat out lying to him, and he wants to, he will push that felony charge and haul you off and confiscate your stuff, or even just a tresspassing or whatever charge to make you go through the drill for your bold face lie to him.
There's no need to lie, but on that hand, there's no need to also openly divulge everything you found either. Depending on what area you happen to be in, even if you 'oopsie' I made a boo boo and are not supposed to be there, no they don't have to tell you, oh well gee golly you have to leave, they can and will arrest you in some areas.
Oh and finally, if YOU, a COP or anyone come up to me and asked me, hey, ya find anything, if I found something sweet, guess what, Im going to tell you NO or I am only going to show you the trinkets. Why you ask, simple, because as you said, yes many of the cops do metal detect and if you tell him, or pretty much anyone for that matter....holy crap dude lookie what I found, next thing you know him and 15 of his buddies are going to be all up in your area cleaning it out. Ive seen THAT happen time and time again as well.