Tired and comfortable puppies bark less, so make sure to thoroughly exercise your puppy and make sure he has gone to the bathroom before you leave. Give your puppy an extra special bone or a Kong filled with peanut butter as you leave. He will be so busy chewing on the bone and will be less likely to bark. Leaving music on or the TV on will help him feel more comfortable while reducing the likelihood of him hearing outside sounds that he may bark at.