I too have the plexi barrier at the door.  As I am not as tall as some, I
prefer the barrier to be less than 24" tall.  Since some ferrets can jump
that high, I have taken a piece of 2" diameter PCV pipe and slit it down
one side, this fits over the top of the barrier and they can't get a grip
to climb over.  I will warn you tho, it did not stop them from trying.
Scamper figured out that if the cat scratching post can be shoved to
within 1=BD feet then he can climb on top of that and soar over the whole
thing!  I just love that boy!
 
Debbie
[Posted in FML issue 3804]