How is the bottom (floor) secured? Also the top? Doors? We ordered a similar pen and while the top and doors had zippers to remove (top) and close (doors), the bottom only had Velcro tabs to hold the bottom and sides together. Way too easy for a clever little dog to scoot out through. We returned that pen and haven't ordered another, but would definitely get this one as long as I knew all possible exits were escape-proof
