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]