perhaps you could buy a "Dutch Door" or one of those doors that open in
halves (first the top then the bottom) that way you could leave the door
open, but not have your ferrets escape.  I don't know how much doors run in
the $'s department, but I am sure your hardware/homeware store may have one.
Or you could buy a small screen door.  They come with clear glass fronts or
just screens you can decide which you want.  But they offer you a clear view
of your fuzzy loved ones and they can see outside without getting into
trouble.  I think you can install those doors inside with no trouble at all.
***********************************************************
Selena Simonetti and "?" [log in to unmask]
"Good.  Bad.  I'm the guy with the gun."--ASH
(Bruce Campbell, "Army of Darkness")
[Posted in FML issue 1418]