I purchased this one because of the top. Previously I bought the smaller Iris pen with no top and my Yorkie puppy managed to scale the sides and get out. Then I bought the large one with the mesh top and she figured out how to get the top off on one side, climb up the top as it was then on a slant and get out. I was afraid she would get hurt jumping down. I tried putting zip ties on the top because the Velcro did no good with my determined escape artist. Well that worked for a while until she decided to just put a hole in it, jump and pull herself up to freedom! Iris does not provide replacement top sadly so I decided to get one with a metal top but hoping to find one with the same kind of detachable bottom since I really loved this feature. Thankfully Iris has such a thing! Unfortunately the door doesn't slide to the side but on the positive side, the top clips on so it is removable and you can just open one half for access if you want. Now mind you, my Yorkie now is 10 months and barely 4 lbs so she did all this when she was a lot smaller! I work in the office just 2 days a week, so she is not in there every day. I do have it set up so her washable pee pads are in there and her potty box. She also eats in there too. I just leave the door open when I am home and she know just where to go. It seems to be working out well and have had it for a few months. The clips for the bottom seem sturdy, although when you pick the pen up, it is heavy. But worth it so I can put the edges of the potty pads in the grove so the pens holds the edges in place.