I was wondering if anybody had any suggestions about a recent problem that
has developed here.  We have two almost 15-year-old cats - DSH, who are
brother and sister - and they have recently decided to occasionally poop
outside their litter boxes.  When they do do it outside their boxes, it is
right in the general vicinity of the boxes, but far enough outside that I
don't think that they are accidentally hanging over their boxes and doing
it.

They have always had their litter boxes in the laundry room, under the
basement stairs - for a little privacy.  However, about 6-8 months ago I
would find the occasional poop on the cement floor outside their boxes.  I  
got tired of cleaning the floor all the time so I put cardboard down under
their boxes in the entire enclsed space under the stairs and that didn't
work for too long.  Then I put plastic over some cardboard (threw the old
cardboard out) but they went on that too!

Their boxes are scooped every day and some days there will only be a couple
of "pee balls" (from the clumping litter) in one box but yet they will poop
outside the boxes.  I have cleaned out both boxes and even rotate them
daily to see if there is a preference as to box or position under the
stairs, but it seems to be totally random.

And judging by the sizes of the stools, it isn't just one cat doing it,
they both are going outside the boxes.  Sometimes they will go a couple
days without doing this and other times it'll happen for several days
straight.  It's very odd behavior.

Anybody out there have any ideas?