I bought The Great Wall (AKA The Pet Corral) play pen for my rats. It is an 18" wide piece of plastic strip as thick as a child's snow sled (the bendable type). It hooks together in any shape or size up to its limit with a velcro strip (which my rats haven't even tried to chew.) It was a little expensive, just under $50 with shipping, but gives my rats more romping space when I can't watch their every move.
My rats are not free range. I usually just hold or carry them. I still think it is important to check up on them periodically and sometimes sit inside the pen with them. I am amazed and complimented by how excited they are by using me as a giant human jungle gym.
My Pet Corral didn't include the bag pictured in the ad. I think it would stand up better on shag carpet than on my hardwood floors. I can easily wipe off my floors, whereas a carpet would be chewed and soiled and harder to keep clean. It tends to lean if I don't put a corner of it on a rug and make the shape more round than oval.
It was worth it for the fun my rats have and the smiles their antics bring to my face.
Manufactured by Milestone Innovative Products Culver City, California (888) 391-3555
All products reviewed become the property of Rat & Mouse Club of America.