To shield precious pets from these tunneling rodents, bury a secure wire mesh basket two to three feet underground. You need a fence that provides an underground barrier and is difficult to climb. Do use a 60 "to 72" barrier. Bury a 24 "horizontal apron a few inches underground outside your backyard.
Yes, this^^^Don't need to bury it. Attach some of the wire to your existing run walls/wood frame, then bend the rest out in an L shape to sit on the surface of the ground. Use landscape staples to secure it in place.
Eh...or not. Wire on bottom of run can damage feet and inhibit scratching.I looked again and it turns out there is wire mesh on the whole run floor underneath the dirt instead. I guess the previous owners of this coop were savvy.