I built a nice kennel on a slab and I bragged and said yeah nothing will get out of this fucker and I went to work the next day and my brother calls and says u better come home lol..Had heavy duty chain link on a slab ..This female crawled under the fence between the fence and the slab their was no gap but she crawled under it.Slab was about 4 inches higher than the bottom of the fence and no gap there but she got under it.Just you and me looking at this you wouldn't even see that as a weak spot that's how tight it was..I had to drive rebar in the ground every couple feet where she couldn't crawl out..And bless he heart she was not a smart dog.