Some adult dogs are not housetrained. If your dog has an accident, it's not because he's incapable or unintelligent, it's because he has not been properly trained. To successfully housetrain your dog, you need to treat him like an 8 week-old pup. The confinement area is your key to success.
Until your dog is perfectly housetrained, never leave him alone unless he's in his confinement area.
He must be 100% supervised when he's outside his confinement area. Take your dog out on leash frequently. Start by walking him at half-hour intervals. If you see your dog sniffing and circling in the house, take him out immediately. Praise and reward him with a treat (dog biscuit) when he relieves himself outdoors. Never yell or punish your dog for a potty accident in the house. See our "Housetraining" handout for detailed instructions.