Since you're not home during the day to correct him, it seems your only choice is to crate him while you're gone or restrict him to another part of the house.

I would clean the area well with an enzyme cleaner and then use one of the product below to keep him away from the sofa. One on the methods they're offering is very similar to a carpet chair mat turned upside down. You might try one of those placed under the sofa leg. Problem is, he may then move to the next available area!
I'm afraid that if he's done this for awhile the odor has penetrated the leather, carpet pad and sub flooring. I'd still clean it, but I really don't think it'll remove all the odor.

Here is a link that might be useful: indoor control

Is your dog intact, because if he is not fixed, you might want to consider having that done. Marking is hard to control, especially with a dog who is home without parental supervison. You have a number of creative ways to solve this. One crate him, which I dont like (personally) you can pen him up in a room with a baby gate (I dont like this either) you can set up something which will make it uncomfortable for your dog to mark the area. You can set up something like a put down a small tarp with some towels underneath it, add an alumium roasting pan that makes alot of noise, which might startle your dog. Or block off the area some how, so your dog can not reach the area in order to mark, when you get home, you can take down the blockade and if you catch him marking you can correct it right then and there. Good luck

There are some who believe that "marking" is a different issue than house training. That said. In my mind, it's all pee, it stains, and it stinks. Therefore, it's a "house training" issue. There "might" be a very minute difference between the two, but if it's happening, and the dog is an indoor dog, it simply must be corrected.

The dog is three, you don't mention how long this has been going on. Theoretically, you have a three year old dog, acting like a three month old dog. He is doing what he want's, when he wants. He has breached your trust for unsupervised freedom. You have severely breached his training by allowing this to happen, beyond only one or two instances.

The "prime potty" training age is between 3 & 6 months. Your dog is well beyond this age. You need to completely back up, and start all over in the potty department, and make corrections along the way. If you do not do this (and consider that it is only going to be temporary until the problem is fixed) it will never get corrected.

There are three things dogs simply must have under control before having unsupervised freedom. They are: Teething, chewing and house training. Without all three of these very basic behavior successes, dog is just not ready, and must have every second supervision when not crated.

SG

Any new behavior such as peeing in the house when previously housebroken *could* be a medical problem. He needs to be checked out by your vet first and foremost. Just because he is peeing in the same place all the time doesn't mean that it is purely behavioral. My own dog had a pretty bad UTI and started peeing by the sliding patio doors. Since she was previously housebroken, I took her to the vets and she had a UTI. Once the infection was cleared, she stopped peeing in the house.

OTOH, If he has been doing this for 3 years, you have a serious problem, because now you have a dog that has to unlearn that it is OK to pee in the house. For 3 years, it has been OK, and now suddenly it's not. It is MUCH more difficult to train OUT a behavior than to train IN a behavior.

I agree with SG on how to manage the problem, if medical problems are ruled out. Crate while you are away, tether while you are inside, taking out for potty so frequently that he never has the opportunity to urinate indoors. There is no unsupervised time allowed at all ever, period, until he has not peed in the house for several months.

Manage it. Don't allow him in the room with the couch. Remedial training as outlined above. If you catch him marking anywhere else, yell NO!!! in a booming, scary voice immediately.

I might get flack for saying this, but dogs see males and females differently, dogs or humans, and they will react quicker to a deeper, booming, "dominant" male voice - so use that to show you are alpha and the only one allowed to "mark" in your home. If you are a woman, practice that "male" voice for corrections.