I have the plastic play pen from wal-mart. It works great! I put Dunks' bed and food/water on one end and his pee pee pad on the other end. But he lifts his legs to pee sometimes so he ends up peeing on the side of the play pen. The play pen is actually made for kids. You can either use it as a rectangular shape or a hexagon (octagon?) shape.
Hope that helps!