Just an FYI, most parks usually have the rules and regulations listed online. Pretty much all of them will have a rule that forbids digging or altering the grass in any way. Swinging a detecting is one thing, but digging holes is what gets people booted and detecting banned.
I was just in a park today with a well manicured lawn with an irrigation system. For 90% of my targets my retrieval method was:
1. Pinpointed the target with my detector
2. Used my Garrett Pro Pointer to precisely pinpoint the target
3. Used a brass probe to quickly find the item, if not to retrieve it as well if shallow enough
4. Pushed in a screwdriver next to the target it to pop out the item
This method leaves no damage and does not attract attention. A few deeper items I had to cut a small slit in the sod and poke around to find them. Any loose dirt that I pull out is placed in a old piece of cloth. When I find the target I use the cloth to put the loose dirt back into the slit, then a light stomp with my foot to finish it off. You can never tell that i was ever there.
There is some real good advise in this thread! Just last weekend I saw some clown detecting in a park. He was carrying around a full sized shovel and digging plugs large enough that you could fit a basketball in them. No pin pointer, so he would spend 5 to 10 minutes pulling his giant plug apart and making a mess, often never finding the piece of metal that he detected in the first place. I went over some of his old holes that had been there a week or so and found trash laying next to them, and in some cases (pictured below) the coin still in the plug or laying next to it

Hopefully when the cops eventually boot him out they don't start targeting others because of him.
