Instead of raising barrier height, we cut a slit in a piece of pvc pipe
along the whole length.  Then slide the pipe down over the barrier (we use
Plexiglas) so that the top of the barrier is smooth and curved leaving no
toe hold for ferrets who would "chin" themselves over the original barrier.
Using this method, we have been able to lower barrier height to one we can
step over more easily.
 
cb
[Posted in FML issue 3418]