Ive been hitting sanded volley ball courtsbut neve more then a quarter or so. Horseshoe pits?
The theory behind horseshoe pits seems sound, but I've never had any luck with them. I've only ever found clad at volleyball courts. It might be that someone else had the same idea as I did and beat me to them.
One theory that has worked for me is starting with the edges of the site. I'm not quite sure why, but most of my finds (and pretty much all of my
good finds) were found at the very edges. I'm not sure why jewelry is so much more common at the borders of public spaces, but that's normally where I find it.
A lot of public spaces around here have been filled, graded, or both. The first time that I hit one of these sites, I walked around and found a back corner that was quite a bit lower than the rest of it. I reasoned that this place had been filled, but they hadn't filled that corner for whatever reason; between its relative seclusion and lack of fill, I reasoned that there might be some keepers back there that had been passed over previously. I don't know if my theory was correct or not but the keepers were there, and only there. Ever since then, when I'm on a site that's obviously had the dirt moved around in the past, I pay particular attention to the low spots.
If your parks are as trashy as the ones around here are, and you can work in heavy trash, take a look at the trashiest areas. Sometimes they've been ignored out of frustration.
I know that it's been said a lot and it's basically common sense, but it took me a while to get it: keep a mental tally of what's in the ground. If I wander into an area (or even a whole park!) where there's nothing in the ground - no can slaw, no bottle caps, nothing - I move on. Parks don't stay clean around here for long and if there's no trash, I know that someone has already hammered the crap out of it relatively recently and they were digging it all, so working it further would likely be a waste of my time.