How bout a weekend class on metal detecting, what you use, how to use it, how to establish permission..etc. Kinda like a hunter education course, or a motorcycle safety course. After you take this course, and pay a ONE TIME FEE you get a card, that says you are licensed to detect and so on and so forth.
I have had to take a lot of theses courses for "certificates" that give me the right to do something. Make a code of ethics, which we already have, as the unsaid rules to go by. If we could just educate people they might see it the right way.
And if anyone asks me why I do this, especially in tot lots, I reach into my bag, pull out the biggest, gnarliest, rustiest nail there is and ask them, "Other than a coin collector, I find stuff like this, I know I would feel safer knowing that this was not in the ground where my child played." That seems to put them in there place. I feel like I am doing the world some justice while I enjoy my HOBBY.
Not only are we protecting a lot of innocent kids from being poked, prodded, punctured, or otherwise protruded into, I am staying fit, by exercising, and making a buck or two while I do.
My rant for the day.