The first thing you need to do with an obsessive behavior is to determine which one of the above probelms your pup has. You have to deal with the probelm before you can get results. But either if your dog's licking is normal or needs medical help, just to be safe I would mention it to your vet.
If you see that you dog is down or bored, it could just be sign of boredom which you really don't have to seek medical attention. If you pay attention to your dog's licking and you see that he is licking alot in a certian place that could be a sign of allergies or pain. In that case you should check with your vet to make sure your pup isn't in pain.
But in the end, if you find the probelm in time and give your dog the proper treatment you can stop the bad behavior and your dog will be as good as new! If you see any werid behavior in your dog, licking or biting please contact me so I can try to help you out and give you some personal tips.