If he is digging under the fence a solution is to burry fence posts 8 to 12 inches down just on the indside of the fence. It's a pain but does stop them from digging under the fence. I know I did this on close to 240 feet of fence. Not a fun thing to do but it worked for the most part. In the long run I think the invisible fence idea is much easier to accomplish and better in the long run.