I had a problem with restricting my crew and wound up, of course, at
the Home Depot. I got a large piece of plexiglass and cut it down to 2
inches large that the doorway to be blocked.

I taped the edges that would be against the doorframe, and "bowed" it
into the doorway -- VOILA!!! Ferrets can see out, but can't get out.
You just have to make sure the piece is tall enough so they can't
scale it.

[Posted in FML 5720]