the city police at their non-emergency number (not 911) & ask if it's OK to detect in city parks, or if you could be fined for it.
I heard a rumor that detecting in St. Paul (MN) city parks was illegal, so called park & rec to ask. I was told law says no digging in parks. I then asked if my screwdriver would be considered a shovel. They said law also said no disturbing the ground. Then they suggested I could try calling the police, so I did.
I asked police person answering the phone if I could be fined for detecting in St Paul city parks. She said that's a good question, I'll go get someone who knows. I was told I might be fined if I left a big hole that could result in injury & said other than that, to use my own discretion. So, in effect, permission granted.
The laws saying no digging or disturbing predate metal detectors, but are often misunderstood as being anti-detecting laws. They are just trying to prevent intentional damage for no reason. While the law usually goes by the letter of the law rather than the spirit (intent)of the law, this is an exception in most communities. Generally, if you aren't doing something that necessitates repair, you're OK. Just ask the police, many of them detect, too! HH, George (MN)