Next - is your cat de-sexed? Male cats who are intact are known for this behavior. It's territorial, and you can't stop it if you don't stop the hormones. If they aren't fixed, do that now.
Another important factor - you must use a cleaner designed for cat urine. It has scents that humans can't pick up, but cats can. If they can smell it, they'll use the spot again. So get the enzymatic cleaner at the pet store.
Do NOT rub your cat's nose in his mess. This only confuses him. He will have no way of associating the point you're trying to get across. It does no one any good, other than perhaps frightening your cat and making him fear you.
If you have no idea what could possibly cause this behavior, try changing litter types. Sometimes it really is that simple, and yes, cats can develop an aversion to a type of litter almost overnight. If it happens from day one - maybe a new box type is also in order. Some cats hate having the hooded boxes, others dislike high sides. It's an easy thing to try, and great if it works.
Do you have multiple cats? Sometimes, for no reason at all, a cat will (after years of sharing) not wish to share the litterbox with its mates. Sometimes, there is a reason (like one of his companions pushed him out of the box) and you just didn't get to see it. So if you have multiple cats and this becomes an issue, add another box to your home.
Coupled with multiple cats or other pets is what kind of escape route they have. Consider this with food as well. If you place their box in a corner, they don't have many ways to get away if another animal approaches them or threatens them. In the box is one of the most vulnerable places a cat can be - that, and at the food station. So maybe the box needs to be in another room, against only one wall, so that if an interloper is spotted, kitty can make a getaway. (This problem is exacerbated by hooded boxes, in case you were wondering.)
Did you add anything to the box? A runner, or a new mat for the entrance/exit? If so, get it out of there, your cat doesn't like it. Did you change the litter type? Change it back. Box size? Change it back.
Did something happen to the cat while in the box? Did someone make a loud noise or spray him with water accidentally while he was in there? If so, you're likely going to have to move that box somewhere else and help him not associate it with getting scared.
Is there something new in the house? Did you just get married? Move? Adopt a pet? Lose a pet? Have a child? Start a home day care business? Get a roommate? Even bring in new furniture? All these things can be very stressful to a cat, who is by nature territorial and possessive. He has his things, his food, his house, and his owner. And anyone who moves in on the territory is a stressor.
A sure fire way to pin that down, other than knowing what is new, is to see if the cat is targeting certain areas. Is he using your new wife's throw pillow and laundry for a litterbox? Then she's the one causing him stress. She will need to gently begin positive interactions with the cat to reduce his anxiety. Have her give him treats, and be the one who puts food down.
Can the cat see outside from where he's doing his business? If your cat is suddenly using the floor in front of a door or window, is he seeing another cat? This is a common reaction - he's marking his house to tell that cat to stay away. He has to have his vision blocked, or the other kitty must be kept out of the yard.
Does he always use the same place or surface? If he always goes on plastic bags, you simply cannot leave plastic bags out. If he is relentless about that corner of the rec room, is it possible to put a litter box there? Later, you can slowly move it away, but get him using the box again.
There is also a medication used for this specific behavior problem that is remarkably successful in stopping elimination problems. Again, this is something you must discuss with your vet and use only under their monitoring.