About the ferrets digging a hole through sheets... I've had a sheet stapled
to the underside of my mattress for something like 7 or 8 years.  What I
found was important was to buy one of the more expensive sheets with the
higher thread counts.  The material is thicker and with the tighter weave
ferrets are less likely to get their claws into it.  Frequent trimming of
the nails helps too.
 
Debra in Fort Worth
[Posted in FML issue 3535]