NEED HELP - Digging Dog - What's Best Way To Stop?

We had an Irish Setter when I was a kid. She was not a hole digger, but liked to dig under the fence and wander thru the neighborhood. My Dad owned a gutter business. He had me dig a foot deep trench just inside the fence and we burried a gutter upside down. Want to talk about entertaining. For the rest of her life every now and then she would have a go at getting out, but never did....