Perhaps a sign indicating that the owner of the property bears no responsibility for any poisoning that results from the mushrooms picked there, might be a deterrent.
Are you anywhere near Girona/Barcelona?
There's no way I could be held responsabile for that. Anyway, they mostly pick just one easy to identify kind, and destroy the rest, mushrooms or whatever. You won't find a single mushroom standing.
I'm a couple hundred miles from Barcelona, and I do get people from there. It's probably around 4 hours drive.
It's not unusual to see over 50 people at once on the property.
First couple of mornings of deer season, I go out and patrol the property lines with my 4 wheeler. I figure the noise of the 4 wheeler let's them know that I'm out watching.
Ohio law makes it illegal for someone to hunt on land without WRITTEN permission. Have you marked your property lines with "no hunting/no tresspassing" signs?
Not enough signs (1 or 2). I will put one every 25 meters or so. Experience in other villages show that signs alone reduce people by 80%. There will be signs mentioning that tresspasing and muchroom picking are not allowed.
I also plan to anulate most parking places with big stones. That will also make it a bit more difficult.
Yes, I will have to patrol the property a lot. I'll have to move there at the start of the season.
In this area, people were very happy with the invasion. They thought that many people = prosperity = money. They start to realize that people is not equal to money but to problems. What you want is few people that spend lots of money, not millions that only leave trash and problems.
They also complain they can hardly make a living, but can't realize that mushrooms are their most valuable asset. Wish I could convince a couple and sell the mushrooms. I might even hire somebody to do so (I can't pick muchrooms for long due to physical problems).