I read two reviews before purchasing this unit which indicated that the only problem both had was that their dog was able to chew through the zipper in a rather short time. But, looking at the prices of other brands, and imagining their structure as best we could from photos, I decided to chance the zipper issue (they all had zippers anyway) since I liked this design. I'm happy I did--even though our puppy DID chew through a zipper! There are two doors with zippers, so I simply taped that one shut with matching Gorilla Tape. On the other door, I now prevented this from happening again: The manufacturer put two zippers on each track of each door (think of a suitcase that can zip from either end). This costs more for the manufacturer, but allows the customer to open only the bottom portion, if so desired (I don't see the necessity of an open pen, but so be it). I simply raised both zipper heads to the top of the pen and bingo! The dog can't reach the zipper head, which it needs to gnaw at for quite a while to break it. The product comes with zipper-on, strong net-topping to fully enclose, which might be useful against hawks if the unit is left outside (though not a good idea to leave unattended). To prevent jumping out, however, it's not really needed since the top sports an inward lip (that can't be "landed on"), like a prison fence, that makes it geometrically impossible to jump over for small dogs, even high jumpers. The flooring is durable and so easy to clean up. Two can be placed together (we bought a second) with doors opened to produce a "train car" effect (just tie a simple cord around the top of the two). Great value and serves its "babysitting," comfortable containment purpose well.