I have heard of cats that use 2 litter boxes. One for peeing and one for poop. Maybe do this kind of a set up and confine the cat to that area for a few days, or as much as you can stand, and see is that helps. Maybe put in two different types of litter, some don't like particular kinds. The heavy scented ones can be issue with some cats. Some cats prefer the fine scoopable, some clay, some, who knows. Clean/scoop everyday. These things w/litter box issues are frustrating. I had one cat that would pee in any box shaped thing left around ie; landry basket, had to store upside down, any kind of box, lid to board game. He was other wise very good w/litter box.
Stupid cat, still loved him, but...stupid cat.

I am surprised that a vet would tell you to put your cat outside more, especially with winter weather, as you mentioned. I don't see how that has any relation to his pooping in the wrong place indoors.

It sounds like you are taking very good care of him, and he is neutered and not de-clawed, all good things.

Maybe being even more careful about cleaning up the litter boxes daily would be the next thing to try. Our cats prefer unscented litter. Also, there are enzyme products you can get at the pet store to remove odor in places he has gone, to discourage him from repeat performances.

Any time my sister has overnight guests or a party her cat poops inappropriately -- on a bed, the sofa, living room carpet, etc. Have there been guests or changes in your home that the cat could be reacting to?

We have a very spoiled tabby, Clancy, that will do this when he gets mad...Usually during the night when one of his sisters takes his spot on the bed....Years ago, we had a black beauty that would go in the tub if he didn't get his way or if we left him alone too long....Does it sound like my fur babies are spoiled???
By the way, we have 3 inside cats and we have 3 litter boxes and they get cleaned every day....

We have one who always poops in the hallway. We tried everything you have done....top of box on/off...different litter....two boxes, etc. The vet said it was a 'behavioral' problem and nothing physical. Hmmmph. We have just dealt with it. He is 15 now. I board dogs (this behavior started years before I started boarding, so not the issue) and am used to an 'accident' now and again. Good carpet cleaners do the trick. Do I like it? No. But again, a nice cat in all other respects. If it was urine he would have been out of here years ago!

Duane

Do you think he poops outside when he is out? If so you could try adding a thin layer of dirt to your litter box. Maybe he likes the texture of the dirt.
There is also a litter called Cat Attract that could help. I added it to our boxes when we first got Cleo and she had some issues. I think I got it at Petsmart.

Here is a link that might be useful: Cat Attract

yes, there is a cat pheremone or at least a spray of some kind out there that attracts cats to a litter box or to each other if necessary.....i've never used it, but i've heard good things about it.....

the most common solution is to lock kitty in a smallish room for as long as you can all bear it.....it forces them to get used to the litter in their toes!! but honestly.....feeding, sleeping and pooping in the bathroom for days is quite a chore in reality.....

dirt from the garden in the litter can work.....i've used that for ferals i've taken in who were never litter trained.....i put the dirt on top of a bit of litter so when they scratch, the litter is eventually exposed.....i use a little less dirt each time, and eventually they accept the litter.....

there are many books out there on the subject....i got lucky with my latest fella and he figured out the litter box before i had to go any further.....but i was actually considering consulting with a behaviourist for $100/hr! i was at my wits end...

i've done a whole lot of reading about 'tellington t-touch' and have had a great deal of success with other behaviour problems in our multi-cat home.....and i'm only just learning the technique.....when i read about the founder's history and success stories with all kinds of beasties, i thought it sounded just too good to be true.....but i've had remarkable results......it's an investment in time and some books from the library.....but cheaper than a consultant.....

good luck

Here is a link that might be useful: tellington ttouch resource

I'm sure you would have mentioned this, but have to ask: does his poop look OK? We once had a cat that started pooping on our beds. Sometimes his poop would have mucus on it, sometimes blood-tinged. Our vet said that he had colitis, and that sometimes cats who experience pain while eliminating will associate the pain with the litterbox and look for other places to go.

Prescription cat food helped greatly - once on it, he went back to the litterbox to poop.