Added benefit; it keeps the rug rats away from the door too.
We opted for a 1/8 inch Lexan panel. I cut it to fit the open side slots and snapped it into place. That holds it in nicely and it can be removed for cleaning.
Only caveat is that Lexan will break if dropped while cleaning. Grrrr.
Sure didn't think Lexan would break by dropping it. We used it in test stands as viewing shields. Have seen it hit with hammers without breaking. Has yours been exposed to a lot of sun? That will definitely make it brittle.