This may more properly belong on my Bethune Catholic blog as it relates to to our small holding, but....
One of our tricks to prevent dogs from digging into our chicken pen is to lay wire or fencing on the ground around the pen.
Here's the set-up. We have a large inner chicken pen which surrounds a chicken yard and the chicken houses. It is "roofed" with either chicken wire or horse fencing. Then, about four feet from the pen we have an outer fence, four feet high.
We have a two-fold anti-digging deterrent system. On the forest side of the chicken pen, we have an old section of chainlink fence laid flat on the ground and semi-secured with moisture barrier wires. Thus dogs (or foxes or coyotes) would have to start digging some four feet away from the outer pen fence to gain access to the inner chicken pen. Between the outer fence and the inner pen we have lined the ground with chicken wire all around the inner pen. Thus, if a dog dug under the outer fence, it would get caught under the wire. If the dog jumps the outer fence, it still can't dig into the inner pen.
All that said, I was doing a little not so random research on the US Patent and Trademark patent data base and found the patent, imaged below.
In case you can't read the "Abstract" on the figure, it reads (my emphasis):
Animals can be prevented from digging in an area by positioning a plastic mesh barrier on the surface of the earth where it is desired to prevent the digging. The mesh can be anchored so that it will remain reliably positioned and will become nearly invisible as vegetation grows through the openings of the mesh.
Who would have thought a plastic mesh would be as effective as a wire one? (The inventor claims it is in the patent.)