I had the same problem with my fuzzies getting into the box spring.  What I
did was very simple and worked wonderfully.  I took an old sheet and stapled
it to the bottom of the box spring.  Make sure to keep the sheet taught and
do not leave any gaps that they can dig at to get into.
 
As a grand finally to keep their attention away from the box spring, I took
an old hammock and stapled it to the bottom of the box spring.  Now when I
walk into the room to find them, all I have to do is look under the bed and
all four are curled up with each other.
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Regards... Russ Hazzon                [log in to unmask]
[Posted in FML issue 1332]