Continue to extend the length of periods until you can leave the pet alone for several hours. Vary the time of your return, so the pet will not expect you to be there at an exact time. Teach your pet to stay in a kennel or run in the yard by moving the crate outside, leaving the crate door open. Once again, leave the pet alone for short periods of time to adjust to its new environment. Ask a neighbor to assist you in determining your dog's ability to handle being left alone.
Some dogs seem to be less affected by periods of isolation.
Others can suffer both mentally and physically. Dogs are pack animals, and will almost always prefer spending time with the family rather than being isolated in the yard. If you are planning on a new adoption or if you currently have a dog, please consider the social needs of the animal. Don't set yourself and your dog up for a disastrous relationship. Using the above steps with a new dog will help it adjust to spending time alone.