My ferrets like digging in the thin layer of usually gray or black cloth
that is on the underside of the box springs.  The easiest way I found to
bed proof is to just flip the box springs over and put the mattress back on
top.  They aren't interested in digging at the thicker cloth on the upside
of the box springs.  I did this at home and I do it at hotels that I take
my fuzzies to.  I can't tell the difference in the way the bed feels when
lying on it.
[Posted in FML issue 3029]