Somebody suggested using mothballs to repell ferrets ( & borax too I think).
But I think borax could be poisonous for ferrets: I recall a recipe to
poison coachroaches which called for sugar & borax.
 
Museums stopped using mothballs because this is toxic: they give off harmful
vapours that can affect humans as well.
 
PS This was discussed several days ago: my apologies if it was already
answered in the meantime.
 
Lorraine Tremblay & the little bundle of troubles (Pepe La Pew), the three
musketeers (Presto, Boum Boum & Snoreau) & the terrible twos (Sanka &
Mukluk)
 
[Moderator's note: Probably thinking of boric acid.  BIG]
[Posted in FML issue 1558]