If you normally spend a large part of the day with your puppy, you need to get him used to being left alone when he is still young. Japanese chins, like all dogs, are sociable animals and naturally do not like being left alone. All dogs will have to be left alone at some point, and it is much easier to start when they are puppies. Otherwise you may have to go through scratched and chewed doors, broken items because he raced around frantically, incessant barking and howling, and ruined carpets from him digging and perhaps loosing bladder control, before you train him when he is an adult.

Start training your chin puppy as soon as you get him. When you see he is getting tired and ready for a nap, play with him a little bit then take him outside in case he needs to go to the toilet. Then put him in his bed and shut him in the room alone. Do not go in to him if he whines, barks, or scratches at the door, it will only teach him that such behavior is rewarded and he will do it more often. Eventually he will accept being alone and settle down to sleep. If your dog is still very young, open the door after he falls asleep, he can then come to you when he wakes up and needs to go outside.

Repeat this many times, slowly building up the time you leave your puppy alone. Do this until he can easily be alone for a few hours.

Never punish your puppy when you come home after leaving for a few hours. Your puppy will not link his punishment with what he did no matter what has happened. He will only be worried about you leaving again, because he links your anger with being left alone and your return.