This is the final result. The puppies are happily napping and the pen is nice and large for them to wander in. It seems to be working well, no one has made a break for it and everyday the pen is exactly where I left it when I come in from work. Seems to be a success after 48 hours. Give it another few weeks and we'll see how it pans out. I still think they are going to think of something we haven't.