These work great!  We have neighbor dogs who also dig under the fence.  All of our dogs get together while we're at work and make their own doggy playdates, working cooperatively to dig giant holes under the privace fence.  They destroyed our fenceline.  These are wonderful, since an electric fence isn't feasible (I can't exactly put shock collars on the neighbor's dogs).  The dogs have tried and tried to dig under these, but have been unsuccessful.  We have two German shepherd mixes and the neighbors have 4 pits; they are all fast, tenacious diggers.  They haven't gotten past one of these barriers yet, and we've had them for a couple of years now.  We ended up buying more to cover more areas of the fence line.  I would not suggest the shorter barriers, because our dogs almost dug to the bottom of these.  I'm sure a shorter barrier wouldn't have kept them away from their friends.