We got a shipment of chicks (they hatched Tues) yesterday, and we're currently keeping them in a 30"x30" box with sides ~ 13" high. I have one of the flaps folded over the top. When do we need to cover the top so they can't get out? They're inside the house, in their own room, so the cat can't get to them. What is a good cover? The brooder lamp hangs down into the box, so it would be hard to put wire mesh or something on the top. I'm open to ideas!