To keep my ferrets confined to the living room (the others just weren't very
ferret-proofable), I just put a thin piece of board in front of the doorway
and leave the door open.  It's just high enough that they can't grab the
top, and smooth enough that they can't climb it.  Just be careful stepping
over it.
 
Frank (and Sebastian and Pris)
[Posted in FML issue 1725]