We live on a property with a large number of ground squirrels. Our chicken run was built with hardware cloth extending as an apron 18" out from the run walls, and yet ground squirrels have tunneled under these aprons into our run and are creating massive holes and tunnels everywhere. I am at a loss as to what we can do to keep them out. They tunnel in every night (we have a security camera in the run and can see them on the night vision camera). I will not use poison. Any other ideas? They are SO destructive.