How do I keep cats from going in baby's crib?

Does anyone know of a product to help keep cats away from the baby while he is sleeping? Like some sort of net type protection thing that can go over a pack & play? I haven't had my baby yet but I was trying to find an item like this that I can put on my baby registry. Does anyone have cats and a newborn? Do they bother the baby? I have heard some bad stories so I'm surprised that I can't find some device meant to keep cats out while the baby is asleep.