The legal system, police, the courts, etc., are pretty hard on people protecting their property...especially with traps. In Leon county, Florida, where this took place, it’s basically a copy of California. Now, imagine one of the neighbor’s kids chasing a ball over a tarp-covered ditch or row of implanted nails. Yeah, the owner would probably be looking at prison time. (Incidentally, amazing they are letting murderers and rapists go because of Covid 19, but arresting people for having a birthday party.)
Colonel Sherburn had it figured out how to cope with that brand of “law enforcement”:
https://etc.usf.edu/lit2go/21/the-adventures-of-huckleberry-finn/171/chapter-22/
The tarp, then, is out...
Just put the signs in the ditch with longer legs...
Oh, I get it; CA is worse.
My thought was to lay a 1x6 in the grass immediately under each sign. Such a placement would be noticeable to a person on foot, who also would be blocked from trampling it because the sign would physically inhibit them stepping on it; whereas a driver, or cyclist, intent on mowing down the sign would be very UNlikely to see the spike strip either before or after running it over.
I think someone else suggested disguising the ditch, and I’d agree that’s iffy, though — again — it could be done in a way evident to slow-passing pedestrians, but not readily discernible to a motorist suffering from TDS.