I've seen the one I think you're talking about, but I don't remember where.
I have this metal one from Petsmart and I love it. With the vertical bars, they can't try to climb out and the bars are spaced close enough they can't squeeze through. The door opens so that I can walk through it when I need to. I usually use mine as an extra large gate, but it make a great play area, too.
Convertible Pet Yard - Gates & Doors - Dog - PetSmart
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He is your friend, your partner, your defender, your dog. You are his life, his love, his leader. He will be yours, faithful and true, to the last beat of his heart. You owe it to him to be worthy of such devotion. -- Author Unknown