Originally Posted by Blackcat31:
I would just limit the number of children allowed to be in one area/center at a time.
It would probably be cheaper and easier than replacing the storage rack. 
I already do that. I allow three in my puzzle/math center. The back of the shelf is up against one of the science shelves. I wonder if bumping into either shelf could cause the puzzles to fall off? I'll experiment with that today.
I *could* purchase one with center money easily enough. We get a relatively generous budget thanks to all the grants we keep getting. There are other things we could use, but the puzzle issue has driven me half insane, I swear.