My coop sits on buried cement blocks and the outside yard is just chicken wire but about 6-8 inches is turned outward on the ground with a little dirt thrown on it. If they dig they will run into the wire.
But my tried and true method is pictured to the left. With her I don't have to worry about my pens, I let them free range everyday, they just get locked up at night. I've only lost two birds in the five years that I've had my Pyrennes. My biggest losses in the past have been other peoples dogs, but we have bear, coyote, bobcat etc., around here also. The woods are right behind my hen house.