I've always had an aversion to closed doors.  In our home the doors on the
rooms are removed - bedrooms and closets, except for the bathroom door of
course.  Lynda and I are ferret sitting and the doors on the ferret's rooms
are normally kept closed when their caretaker is home but we leave them
open when the ferrets are caged.
 
What I use at home for doors when needed, is a piece of plexi-glass cut 1
inch larger than the door frame and about 28" high, better to go higher
though if you have a jumper and be sure not to put anything near the
doorway that the ferrets could climb up on to get over the top.  The
plexi-glass allows us to see in at all times and to monitor the temp in
the room.  I use this on the bathroom doorway while I'm gone to keep the
dogs IN the bathroom.  With the dogs I have to use 2, one on each side of
the doorway as the dogs tend to push on it if there is only one.
 
I buy the plexi-glass at the local hardware store and they cut it to my
size specifications.  Some stores carry different thickness too.  You won't
want it too thick or it won't bend easily.
 
Just a thought for anyone that has a separate ferret room that they
normally close the door to.
 
Hugs to all. tle
[Posted in FML issue 2763]