I have plexiglass on the back of my ferret nations. they are up against the wall and it helps with the shavings/hay/poo falling behind. it still falls on the sides, even those i have metal pans.
the way mine is attached, the chins can not even get to it. and since it is only on the back it does not restrict airflow BUT it is a pain to adjust shelves without drilling holes in it and when you decide to rearrange, than you have more holes. the plexi i have it dark tinted so you can really see thru the back which i like.