Blades67: Wonderboard (I believe thats the name) would easily change a closet into a secure area. Basically, its like sheet concrete, you have to predrill the nail holes because there is no way you could expect to hammer through it. Put one layer on the inside (its fire resistant too, IIRC), and another layer on the outside of the closet. This stuff is what they use in the high schools so that the kids cant destroy the place.
Kharn