What to use to keep things from digging under pen?

[crews28]

I got some things trying to dig under my pens. I have used posts laying them flat down across the bottom of pen.
I tried wire on outside to

 

[aart]

Mesh Aprons.......mesh on corners is out of scale in graphic, but son't forget the corners!

 

[luvmychixandducks]

Go on Craigslist look for free chain link fencing.
Zip tie to bottom of your existing fence and lay on grass like picture in previous post response.
The fence will sink into the grass so you can mow right over and diggers aren't smart enough to back up the necessary distance to get under the flat fencing.