I bought 3 of these exercise pens.  I hooked them together and it made a large play pen for my twom Mini Schnauzers to romp and play in.  They love it and I love it.  I have an extra 16 ft. of play space by using pens on three sides and outside wall of house as the fourth wall.  I'm going thru treatment for a bum knee and soon to have back surgery.  This is a life saver for me, and my boys get plenty of exercise, running and playing in it.  Ty