A few months ago I was given permission to hunt an old school site on the grounds of a church. My wife and I had an incredible hunt – several silver dimes and some good jewelry.
Anyway, I return several days later for a quick follow up hunt and see that many of our plugs, even some of the discreet "u-shaped" ones in the grassy areas, were "re-dug". Dirt and the grass layer were removed and laying next to the open hole. I was horrified. If anyone had seen this, it could be extremely embarrassing.
I determined that animals such as armadillos at night and squirrels during the day will remove your plugs because they can smell the disturbed soil, and it is simply easier to remove your plug to forage than to dig a new hole.
If your area is prone to this issue, where possible, especially on manicured property, return the next day to make sure the site is as you left it. An embarrassing call from the landowner can kill your permission, reference and networking opportunity for other sites.
And think about how pathetic you are going to sound when you blame it on small animals and the angry landowner hangs up on you!