Both of my small dogs lick the bedspread and the couch excessively. Why and how can I deter this behavior? We haven't really tried anything except shooshing at them and placing them on the floor to stop it.
It seems to me that this is obsessive behavior. I think that they need a combination of more mental stimulation and an alternative to lick, with a correction if it persists.
Step one, would be to exercise your dogs more. They are getting some exercise when they play fetch, but it's probably not enough and it's also mindless. They don't have to do anything but run get the ball, bring the ball back. You need to find something that challenges them mentally. There are several things, but trick training or games would be an excellent challenge for them mentally. For instance, what if you bought some small cones and hid the ball or a treat under them and taught them to knock them over or scent for the item before bringing it back? They'd have to stop and think about it, even it it's what cone to start with. This kind of exercise that requires mental effort will drain them much more than simply throwing a ball. Like Huangism said, Cesar Millan has some good advice and his 'pack walk' is associated with the mental part of the exercise.
Next, I'd offer an alternative. I'd suggest a kong filled with peanut butter (frozen if they empty it too quickly. This can channel better than an hour of licking. Raw hides and other chew toys would also channel the mouthing behavior.
Lastly, I'd start implementing a correction if these other things don't work. I don't mean spanking your dog, but firstly, breaking his attention. Dogs get focused in on something and just drone on it, like barking. You need to break the cycle. I'd ask them to stop that and come do a command, like sit. I'd then treat them and leave them alone. If they seemed engaged, I'd keep training. The point, though, is to stop the behavior and get their mind on something else. If they ignore me, I'd separate them from the object they're trying to lick. I'd put them down off the bed or out of the room.
I know you probably have a full day between work and your other responsibilities and you just want to go home and relax. However, you have to make sure you see to your dogs needs as well. Whether you wanted to go or not, you got plenty of mental stimulation at work. He got the equivalent of staring at a wall the entire time you were gone. We as people get all kinds of stimulation, from work, to eating go food, radio, tv, internet, etc... It's very easy for us to lay around and unwind. However, your dog get a lot of that with you gone, so he's ready for his stimulation when you get home and even though you just want to sit down, you'll need to put the time in for him. As of writing this, I'm most of the way through my work day and I'm exhausted, but I think I have a horse with an abscess at home and I'm going to have to go home and deal with that. I don't want this part of the answer to seem like I'm criticizing, because I'm not. You may spend a vast amount of time with your dog. I just want to make sure you're seeing it from his perspective. Good luck.