Cat does not always use litter box, he goes on the carpet.

I have been trying to fix a cat urination problem for quite a long
time. I'd like to replace the carpet in my living room, but I don't
want the cat to urinate on it. So, I'd like to fix the cat problem
first.

He is a 5 year old male cat. He is fixed and never sprays like some
people talk about.

I have two litter boxes for my cat, one is in the bathroom and the
other is next the dryer off of the kitchen. I empty them every few
days. He uses these litter boxes on a regular basis. However, he also
may go on the carpet or even at times defecate on it. And once he does
he tends to visit that spot more frequently until I treat it with an
enzyme product. There are two particular areas in the living room that
he likes to do this on, but these areas are not exclusive. He always
goes next the wall, never in the middle of the living room. He also
seems to prefer places that are behind pieces of furniture or in a
corner. This always happens down stairs, never upstairs. I've treated
these areas with several types of enzyme products (in particular:
Enzyme D by Big D Industries). It helps for a while, perhaps because
these spots are wet and don't smell good, but it happens again and I
start the process over again.

Also, recently I have removed the carpet and padding from one
particular problem area. I threw the padding away and I soaked the
carpet and sub floor with an enzyme product. Then I painted the sub
floor with an odor sealer called ‘Kills'. However, I caught him in the
act at this location the other day.

What can I do to train him to always use the litter box?
Any good books?
Any good web sites?

Please respond to this newsgroup.
Thanks,
Brian