Q: Our 18-month-old male Labrador lifts his leg on the corner of the living-room couch. He does not go anywhere else in the house. Any suggestions?
A: First, is your dog neutered? Male dogs live to mark territory, but neutering cuts down on this unpleasant, hormone-driven behavior. It also makes the animal a safer, happier pet.
Second, clean up the area where the dog is marking, using enzymatic cleaners designed for pet messes. (Other kinds of cleaners do not eliminate the odor, and some, like ammonia, even make the problem worse.) A thorough cleaning is essential, since any remnant of past mistakes will emit an odor that will attract the dog to refresh his mark. What you cannot clean, you must replace.
Finally, block off the area from the dog while he's being retrained. Take the dog outside and praise him for marking in the right spot. In the house, keep him on leash for the next few weeks so he never gets the opportunity to make the wrong decision.
If you catch him in the act of lifting his leg indoors, clap your hands to distract him and stop the behavior. Then take him outside to finish the job, praising him for getting it right. Punishment is never necessary and is flat-out useless if done after the fact.
After a few weeks, if you don't think you're getting through to your dog, ask your veterinarian for a referral to a veterinary behaviorist. These are veterinarians with additional training in resolving behavior problems in animals, and they combine a proven scientific approach with medications that will help in the retraining period.