I coin hunt a local town park and can give you a few tips at keeping the maintenance crew on your good side. I use a very curved, long and narrow trowel designed for transplanting bulbs. Maybe $5 from Lowes. Has a rubber handle and even a calibrated depth scale on the blade. I cut a vertical plug, and then lay it on a sheet of plastic (mine is an old calculator cover). There's a reason for this. It traps the dirt, so after you find the coin ~ a little electronic hand probe is a big help, especially if it's still in the wall of the hole ~ so you get it all back in the hole before replacing the plug. It also prevents a pile of dirt on top of the grass. If you leave that when the dirt dries it LOOKS like a dead spot in the grass.
Another thing I have found to keep on good terms is to carry a gallon pail in your trunk for the trash. I pick up litter and any metal I dig. This goes in the pail. I once had the town maintenance superintendent come over to talk as I packed up. He was impressed with the pins, razor blade, last 3" of a knife, broken glass on a light-bulb base, etc. that I had pulled out of the grass. Since then I've had other folks come over to talk (those as are nice enough to wait for you to finish instaed of try and walk along talking - with my Black Widows I can't hear them, anyway) and they seem impressed that I am finding harmful stuff and not gettin rich off the town. 57? in dirty clad doesn't look too fabulous to most folks. I never completely empty it of the nasty stuff.
Also, make sure you take the first ring you find to the town office and put it in the lost and found. I do this with any good rings anyway. It keeps you in a good light, as some folks equate park detecting with stealing (I've been told that to my face). Usually you can pick it up after 90 days anyway, and if you do get a match-up you are a hero for a week.
I don't use a coin probe to pop coins because a scratch is enough to lower a good find 30 or 40 grade points (on the 1 to 70 scale), equal to two or three grades, which can be 85% in collector value. Ouch.