I bet they are all good IF metal detecting is allowed. Ask the park manager/parks and recreation manager or check online to see if you are permitted to hunt there. Try parks closer to rich people's neighborhoods.
With all due respect for curlys-gold, do NOT go ask a "park manager/parks and recreation manager " if you can detect the parks. Go with his 2nd option/method, which is to look up muni codes, park rules, etc.... for yourself. Because if you ask a live person "can i?", there's been too many cases of bored deskbound bureaucrats telling an md'r "no", when in fact, no rule really says such a thing. Just because they morph something else to aply to your "pressing question" (when in fact, they'd probably have never noticed or cared). So look it up for yourself, if you are skittish.
And so you know, gold coins are sort of the "holy grail" or "hole in one" find of md'ing. You're not likely just to walk into a long island park, and start "finding gold coins". You'll dig HUNDREDS or THOUSANDS of silver coins, before you'll ever get a gold coin, is usually how the ratios work. There's good hunters who've gone there entire careers, and have YET to find a gold coin. Others have found perhaps a few, in many many years. Yes they can turn up anywhere you're finding 1800's coins, but I'm just saying, they're not a common fumble fingers loss