A good way to train a puppy is to confine him to a dog crate when you can’t supervise him. This will not only keep him out of trouble and help housebreak him but it will help him feel safe. Dogs dig dens in the wild to create their own place to sleep. A crate serves the same purpose for domestic dogs. If you get your puppy used to his crate while he is still young, he will grow to love his crate as an adult. Just make sure that you never keep your dog in the crate longer than overnight.  To make a dog feel secure, his crate should be quite small.  Small enough that it should feel like his own den.  It should be tall enough that the dog can stand up, turn around and lie down with a straight spine. If your crate is too large for your puppy, you can fill the extra space with a box until he grows.