Have you tried plexiglass panels?  If you have your measurements, you
can usually have them cut to size and framed for your project.  I have
had several done at the local glass company.  They do a good job and,
it is not that expensive, and it dows not look that bad.  BEtter than
cardboard, or chairs pushed into corners..
 
Marilyn
[Posted in FML issue 4899]