Hi Anthony,
 
Sounds like you've heard the drill about putting bedding in each corner,
food dishes also are good deterrents.  However.......they didn't work for
me.  I have one ferret (Meep)who likes to use ferret litter in the box, and
Daisy who likes to use newspaper (I think she doesn't like sliding around
when she is trying to do her business - and she does seem to slip more than
our male).  Now we put newspaper under the litter boxes so that rims around
the edge about 4-6 inches and she backs up to the pan and uses the
newspaper.  With the newspaper she is about 95%, before with the litter
boxes and no newspaper she was about 40%.  So....maybe you could try using
newspaper either in the corners he uses or in the litterbox itself.  I
finally decided balling up newspaper and tossing it was easier than
cleaning up corners.  We also use newspaper in one corner of each room
Daisy is allowed in.  She has of course "picked" her corners on previous
occasions so this was an easy way to train her.
 
Karla
Meep and Daisy
[Posted in FML issue 2781]