jimzz977, more things I noticed implicit in your story:
a) From 6:30am to 7:30am (the first hour), you had no problems. Right? You detected to your heart's content, and no one cared, right? It was only after some of those radio control airplane people arrived, that any "problems" started. I know you said you kept your distance from them (that was logical), but the point still remains: Sometimes our best times to hunt spots, is low-to-no traffic. Like that first hour you were hunting.
b) you say "some guys were pointing in your direction" (to the cops?) is when the problem started. Sounds to me like it was the radio control people who called the cops. Then put yourself in the cop's shoes: They get a call from someone, and have to show up. Now they have to "please mr. or mrs. griper" . They have to make their trip all the way there have some merit. So they boot you. In other words, if that SAME cop had been just happen-chance driving by that park, perhaps he personally wouldn't have cared less! It's only upon getting a call, and have to come out, and mentally go through some silly exercise of whether or not "something is allowed" or not. Again, this sounds like point (a) above, that the best times are out-of-site-is-out-of-mind. I do not equate the booting by a cop, if I know the reason he is there is because some dog-walker or kite-flyer called, to automatically mean: "therefore, detecting is not allowed". Because a lot of times (unless the cop cites some actual real & specific "no detecting" rule), they are simply appeasing a griper. So you let that park "take a break", and merely go back a few weeks later. Oh sure, be sure to avoid that one dog-walker or kite-flyer from then on.
Because there's no escaping the connotations that our hobby has. That you "might hurt the grass" (even though YOU know you won't, yet anyone can level the accusation if they're in a bad mood).
So I've gotten to where I work parks, when I can, at the most vacant-of-times. Even at night for pete's sake. Not necessarily because "it's not allowed" or that there's any rules, but simply ........ well ........ you gotta treat this hobby like nose-picking: not illegal .... but .... we all sort of use a little discretion in our timing.