We have a total of four cats and three litterboxes.  I have read and been
told that you have to have a seperate one for each cat, but I have witnessed
the three younger cats mixing and matching.  The oldest one *used* to use
the litterbox.

She is around eighteen years old -- used to be hell on wheels, has softened
in her old age but still has a mean streak.  I didn't know cats lived that
long.  She's gotten a little weaker, she doesn't bound up onto high surfaces
anymore.

Lately the problem is that she has been finding out of the way places to
soil.     I had to muck out behind a giant tv cabinet that is diagonal in a
corner and reposition so she couldn't get back there.  Now I'm finding
random puddles of urine in corners and more distressingly behind the couch.
Against the wall, it's an easy cat tunnel.  I've considered rearranging the
furniture again to eliminate the hidden areas where she will urinate and it
won't be discovered until there's a smell.  We have a natural wood floor
that's starting to discolor in her regular areas.  Behaviorally I'm sure
it's possible that the younger cats are now establishing territory and
pushing the older one out.

I've tried the dog trick of showing her the puddle then taking her to the
litterbox.  I know this probably will have no effect as cat brains are that
much more complicated and stubborn.  Another thing I'm now considering is
fashioning a new litterbox.  The current ones are enclosed with high sides
that I'm wondering if she's having problem stepping over the wall.  While I
have no desire for a litterbox in the living room, I'm wondering if I made a
shallow one out of a low cardboard box and put it where she goes if she
might take to it again.  Then if I gradually shifted it out of the living
room she might take the hint.

Any suggestions from anyone who has had a similar problem or who understands
how to manipulate the stubborn feline psyche are much appreciated.