As acids go, boric acid is very weak.  A dilute solution of boric acid is
commonly used (by people) as an eyewash.  The solid is a white powder,
and probably tastes very nasty.  I really doubt that a ferret would be
interested in it enough to ingest a harmful portion, but then again, it's
always better to be safe than sorry, I s'pose.  Of all the pesticides you
could use, however, boric acid would probably be the least harmful to
your pets.
 
Jen
[Posted in FML issue 1339]