This always an interesting subject that seems to bring out all the dire predictions of jail if you detect public property without getting permission from somebody in authority. Private property? Absolutely, get permission. Public property has rules and regs governing that plot of land and it's available to anyone who wants to view them, either online or at the city/county courthouse. There are gray areas where we might get a rule applied to us when it really wasn't meant to prevent metal detecting. I've had many encounters with LEO's over my 49 years of detecting. Most are cool, curious about what you've found and just explain that they are responding to someone's complaint or concern. If you've been making clean recoveries and are friendly and polite, usually they just wish you good luck and are on their way to more important duties. Sometimes you get what Clad2Silver mentioned.....the Barney Fife. Usually a rookie still feeling power drunk. With those, it's best just to be polite, don't argue, and move on to someplace else. We here all know the absurdity of painting us with the same brush as a vandal or thief, but, those who are unfamiliar with our hobby might not see that absurdity. Here's one encounter my friends and I had one time in a local park.
It's an old park. Old coins and relics have been found here, so, we love to hunt the place. There are condos next door and there apparently is someone living there overlooking the park that thinks the park is not public and belongs to them. Not true of course. We've researched the place and reviewed the rules before we first started detecting there. So, we're busy having fun detecting on a cool winter morning the day after we had a pretty decent rainstorm. The ground is nice and soft, we're getting good depth on our machines, and finding some 100+ year old coins. Suddenly, a police car jumps the curb, over the sidewalk and comes ripping through the park right up to where we're detecting. Out pops the driver and his partner with the attitude that we're all on the FBI's most wanted list. They start reading us the riot act about violating the law and that we would have to leave or be arrested. We're polite and explain that we've researched all the rules regarding this park and didn't see anything preventing us from enjoying our hobby there. We also asked politely if he could explain which law we were violating and cite chapter and verse of where it's written. Well, that kind of dumbfounded them both, as they didn't know, but, they had a complaint and they had to respond. We kind of insisted on knowing as we wanted to avoid this problem in the future, and would they be so kind as to find out. While we were waiting to hear from the higher ups, we discussed our hobby, explained how we made recoveries, asked if they could see where we'd made any (they couldn't), etc. Well, half an hour later and repeated calls between them and headquarters, they finally said it was under the "damage, alter, deface" general rules that are part of every public place in America. These weren't recent laws directed at us or our hobby, but, meant to prevent people from defacing or destroying picnic tables, drinking fountains, benches and the like. It also was meant to keep people from removing plants and grass to landscape their own property. When the word came over the police radio, it was loud enough for all of us to hear. At about the same time my friends and I, along with the cops all in unison looked down to see the 8" deep ruts that the patrol car had made in the grass while driving though the park that day after the rain. They had this sheepish look on their face, got in their car, and told us to continue our responsible ways as they drove away. Soon as they were out of earshot, we busted up laughing and continued on detecting the rest of the day without incident. The bottom line is that if you're going to stay in this hobby any length of time, and are going to detect public property, you're going to encounter people who complain about what you are doing. Oh well, you're just going to have to decide to either only hunt private property with permission, roll with the punches on public property, or give up the hobby.