If you keep your dog in a fenced in backyard, chances are that he’ll try to dig his way to freedom. Dogs often dig under a gate, since there’s has a gap under it to allow the gate to swing open.
To prevent your dog from digging under a gate:

• Cut a pressure treated 4” x 4” landscape timber so it fits tightly between the gate posts.
• Dig a trench across the gate opening as deep as the thickness of the timber.
• Position the timber in the gate opening so there is just a small gap between the timber and bottom of the gate.
• Secure the timber in place by toenailing galvanized nails or screws through each end of the timber into the gate posts.
• Backfill the trench with dirt so the ground is level.