It sounds like your cat may have a substrate preference for what he likes to eliminate on. Also, there may be some anxiety component to his problem. If there are any new animals, new people, move, etc. going on, he could be upset by this. My cat pissed on two spots of our new wood floors - she hated the construction!
To test, shut him up in a tiled bathroom. Put several trays of different litters, also some trays with shredded paper, towels and any other substrate you can think of. Some cats like regular sand instead of litter. Get creative. After 24 hours, see where he like to go the most. Try to get it down to a couple. These may be your new litter. My cat loves to pee on towels and laundry.
Also, make sure that you have at least 3 litter boxes in several different parts of the house so he can get to one easily at any time. Make sure that they are away from any dogs/kids/disturbing areas.
Make sure your cat has had a urinalysis with a urine culture perform to rule out any infections/crystals. Also have a blood panel run to make sure he is healthy.
Lastly, you can try some antianxiety medications. There is one specifically labelled for cats but some human antianxiety medicines have been used offlabel for these problems. Talk about this with your vet. IF you vet is uncomfortable about it, see a veterinary behaviorist.
I hope this info helped you somewhat. This can be one of the most frustrating cases for us too!
Dr. Amanda
Edited by DrAmanda on March 27 2006 at 5:52 PM
Dr. Amanda
Small Animal Veterinarian
Special interest in canine and feline behavior.