Keep hitting that old park! You've probably already detected there around old trees or stumps where people have lounged & maybe lost jewelry or older coins. Whether in old park, field with crumbled foundations, or a piling & boulder-infested beach, many of my son & my best finds occur when we detect RIGHT UP AGAINST CURBS, COLLAPSING FENCES, FOUNDATIONS, ETC. -- so give that a try in your park if you haven't already. It's slow work detecting right up against those features due to their often having nails or rebar included, but your results can be wonderful! Under a rotting fence at a wood's edge, my son dug his gorgeous 1848 silver dime & I unearthed a very old silver rosary. Plus our first gold rings were in rocky, junky locations! HAVE FUN & KEEP POSTING!
Some of mine look worse, came home one time with half a corroded modern penny and a hand full of pull tabs, not even the colorful ones! The great thing about this hobby, your next signal, could be "The One".