My little girl climbed out of her pen the second night we had her as a tiny pup. I found her the next morning sleeping inside my slipper next to the bed! I found a black wire top for the pen online. I had to shape the pen into a 4' x 4' square, but the top fit perfectly and did the trick! Before the top came, I actually caught her climbing the pen. She was hanging on in a corner of the pen by her front paws, and her little back legs were swinging back and forth trying to get a foothold. It was actually pretty funny looking!
I had to put a tarp over the top of the pen until the top arrived.