Yes I too have an 11 year old part maine coon tabby..I posted before about him... You're absolutey right, when you catch him in the position.. and repremand him.. he knows he's doing something wrong.. and runs to his box.. he's done this since he was a kitten.. I'm sure it's a territorial thing.. because the rest of his day is spent marking things with his chin.. I have even tried giving lots more attention.. but he just seems to be the same.. It's really annoying, but I love the big guy too much to put him down..