Mega B, problem with your reply is .....This Is AMERICA!!!!! We left England a long time ago, and we are a republic of free citizens. We the people own the schools, the parks, the court houses, the city and county property. Most public property is open game around here in the states. All we have to do is go to our local city/state websites and see what the posted rules are and follow them. Some areas where heavy detecting activity has already taken place, there may be rules and laws like probe only. (Usually because some nincompoop left a bunch of open holes or a mess) and ruined it for others. Some cities like the one I live in is still friendly to the hobby. But with that said, sometimes when Barney Fife , (The local constable) is called he may use another law like vandalism or damage to public property, to describe digging for a coin and issue a misdemeanor ticket.
I do agree, getting permission and avoiding confrontation at all costs is usually best. Respecting the condition of the property is crucial.
For instance: I wanted to detect the local high school football field. So instead of thinking it's my right to do it as a local citizen, I asked the grounds keeper if it would be ok. He simply replied that would be fine. Permission also involves educating people in what the hobby involves, and can be key to getting permission. We all have seen the story board pictures of what "my parents think I do, what I think I do, and what others think I do, and what I really am doing". Perception is key to communication and we all have to live together, so when we talk with people and communicate what our intentions are, we all get along better. When we get some no's along the way, be patient the next yes is just around the corner.
I will say, I do like the treasure trove process across the pond. I notice that you get to split 50/50 with the land owner you got permission from, and when the local museum buys the treasure, and you keep it all. Here in the states there is a terrible tax both state and federal. Remembering the couple who "found" the gold coin stashed in cans in California. Supposing the cache fetched 10,000,000, they would pay an estimated 5.7 million in state and federal taxes. Sounds like you have it better in that situation. Sometimes it still feels like were governed by the king, here in the states. I guess I should say, were still, mostly free! Happy hunting!