I probably should have just gone
Yep, you are probably right, maybe you should have. I hope I'm wrong, for your sake, but I doubt you'll ever get that email, or not the one you want, anyway. It's just too easy for people, that don't have a clue, to simply say no, even though there is really no ordinance or law prohibiting MDing on those public lands, assuming that's what they are.
Every situation is different. Heck, I metal detect behind my house, on a golf course, where I live. Yes, it's a small, semi-private club, not to awfully busy, but most people know I live here, and all I've ever heard from anyone is (even from the club manager), found anything? Never once, has anyone asked me what I was doing. Yes, I'm somewhat discrete about things. I usually start out in my backyard, and just ease on out onto the course, as the situation permits. I don't go out there on the weekends, during tournaments, or any time that the course appears to be busy. When I do venture out, I stay off of the tee boxes, out of the fairways, and off of the greens. Living here, I kinda know when the slack times are, and I tend to venture out at these times. Again, every situation is different. I'm sure if a couple more detectorists decided to show up, it would all be over, but, so far so good.
Also, it's sometimes better to simply beg for forgiveness, than to ask permission and be denied. Now,
before everyone starts jumping up and down and pointing fingers, I DO NOT, in any way, advocate this as being the proper approach to accessing spots to MD, but again I do emphasize, "every situation is different", and must be read differently. You are the one in the best position to make that call.