Marion:
 
Are you sure you mean chicken wire?  Chicken wire has rather large oval or
nearly round openings, openings any enterprising ferret worth its name will
find a way to attempt to pass through -- and possibly become trapped, with
tragic consequences.
 
Perhaps what you mean is hardware cloth.  This has square openings, far
smaller than a ferret's head, and therefore quite risk-proof.
 
Good idea, though.
 
Al Wiebe
[Posted in FML issue 3028]