We have used portable exercise pens for years. With two larger dogs, we actually used two fastened together to make it larger. Both dogs could put their heads over the side of the fence, but both knew that putting feet up or trying to go over the fence was a no-no. Never left then outside in the pen unless one of us was with them. Only problem was others dogs, leashed or un-leashed, coming up to their pen. Amazing how you can tell others that the dogs did not like other dogs around the pen, and they would still let their little foo-foo come right up to the fence. Thankfully, none of them ever got eaten.