Why not be creative and make a top-piece for whatever you use for a
play-ing pen?
 
Suppose your play-pen is a nice, sturdy collapsible dog-pen,like the ones
used for folks going to show their pups at dog-shows, and you buy a piece
of plywood , or two, if you might like to get two pens and join their
ends to make a play-pen "double-wide" :) (I like this idea, I'm gonna
make a pair of these for our rabbits that keep coming from another county
shelter's over-flow and we adopt out for the "fee" of a bag of no-dust
litter)...but anyway, fit you a piece or a whole sheet of plywood to your
penned area and (this is important for either ferrets or rabbits) weight
this down!  A cindeblock-brick (a pair or three of them balanced around
the plywood sheet would be safer) for a few cents more, when you go get
that phywood sheet would do it.  Then, the wider you can make your
playing pen, the more playing stuff you can put inside it...like the
FML-famous rice-filled playing box.  howzzat?
 
(Susie Lee at the Ferret & Dove Sanctuary in Pensacola, Fl.  see our
fuzzy all-kinda-critters here...
http://www.angelfire.com/theforce/ferret_rescuer/index.html
[Posted in FML issue 4289]