Wow I feel blessed, haven't been harassed much at all.
One time I was hunting property of Ford motor co, one of those giant fields and all they ever use them for is to grow sunflowers, and 1,000,000's of them, a few months a year. Pulled a civil war token and a couple 1800's quarters, was really liking this spot when one day I was in the zone digging up a find and out of the blue a loud voice says "WHAT ARE YOU DOING ??" I nearly jumped out of my boots and swung my detector, last thing I expected was someone walking up on me in the middle of a field, and I usually have superior situational awareness.
Of course, I felt like saying "What the hell does it look like I'm doing ?" but I just said, I'm metal detecting. He said oh, can't do that year, ford motor company does not want you here, this is private property you are trespassing and you are going to have to leave. Another fat rent a cop was taking my license number ,,, So I said ok, see ya and left.
[Thing is, year before I hunted the same field and an older rent a cop, retired cop was security, and he was real friendly and said he didn't see any problems with me detecting a plowed field - Even told me to use caution as they spray the field with pesticides].
But these younger rent a cops are the opposite. So I figure I'll come back on a Sunday when they will be understaffed and not so vigilant. I was wrong, same rent a cop was on me within 10 minutes he said, oh you again, I thought I told you you weren't allowed here and not to come back. I said oh well, must be losing my memory or something. He said real funny, leave right now and next time I'll call the cops and have you arrested for trespassing. I said do what you gotta do, I'm sure a guy metal detecting an empty field will be a real high priority run for them ,,, He then gets in my face and said you have a hard time hearing ? He was about to do a chest bump, I said take a step back jack, you put your hands on me and its on. I'm not going to play internet tough guy here but I have been in lots of brawls, have won most and I generally don't look like the type of guy to be messed with.
Even though he had another rent a cop with him he called for backup, "Charlie 4 this in Tango 5, request backup in lot 4C and request you call police for aggressive intruder" I was like oh sheesh, I did an eye roll and face palm, walked to my truck, put my gear away and drove off without further ado.
After finding that civil war token I was stoked and still was not to be put off, so I figured I'd try a night foray with a headlight. No rent a cops but mosquitoes were out in droves, never expected them to swarm an empty field and I have no idea what they feed on when I'm not there, but I was doing more swatting than swinging. I stopped to investigate a promising signal and it was like every mosquito within a mile radius knew I was there and wanted a piece of me, they were biting me everywhere. I shone my headlight beam into the air and I could actually see them forming landing patterns towards me, then one flew in my ear and bit there and I said screw this, this is worse than rent a cops, I actually ran out of there with them in hot pursuit, even flying into my truck and I was still swatting them miles down the road.
So that was about my only run in, thing is I know they were technically correct and just doing their jobs I guess, but they were overly aggressive and pompous, and the older guy from 2 years ago gave me the impression I could detect there no problem ... So it looks for all practical purposes there is no way to detect that area. [Did some research and found out that whole area was once a home for orphans of the civil war, history buried in those fields could be astounding and by the decree of Ford himself, it always was and always will be open fields, was never anything built on it except the orphanage and never will be.]
