Seperation Anxiety occuring in Dogs

Dogs with separation anxiety exhibit extreme behavior problems when they are left alone. The most common behaviors are destruction of property (sometimes injuring themselves in the process), especially around doors or windows, howling and barking, and urination and defecation from distress. The destruction and house soiling is not an attempt to seek revenge on the owner for leaving, but is actually a panic response.

Separation anxiety sometimes happens when

A dog has never or rarely been left alone.
Following a long interval, such as a vacation, when dog and owner are constantly together.
After a traumatic event (in the dog's mind) such as time at a boarding kennel or shelter.
After a change in the family's routine, like a move to a new home, or a new person in the home.

Dogs that exhibit separation anxiety follow their owners around from room to room and become anxious even if a closed door separates them from the owner. They dislike spending time alone outdoors. They act depressed or anxious to your getting ready to leave the house.

For minor separation anxiety problems the following may be helpful:

Keep comings and goings low key. Ignore the dog the first few minutes when you come home, then calmly pet him.
Leave your dog with an article of clothing that has your scent on it-- one that you don't mind if it gets chewed on.
Provide enriched environment to keep the dog busy while alone. A Kong toy (even several) that is stuffed with soft food is good-- unstuffing it will occupy the dog. Hide favorite chewies in the house for the dog to find.
Sometimes leaving the radio or TV on is helpful, if the dog associates it with your presence. Or make a tape of family kitchen noise and play it while you are gone.
Provide aerobic exercise before leaving, but let the dog calm down before you leave. A tired dog will rest better.
Teach a sit or down stay (or use a tether) and gradually increase the distance you move away from your dog. Your goal is to move briefly out of sight while he remains in position. You want your dog to be comfortable about spending time apart from you.
Some dogs may be more comfortable in a crate - if the dog has first been trained to regard the crate as a safe haven. However, in many SA cases, confinement only worsens the dog's panic and hysteria.
Some dogs do better if they have a companion animal to keep them company. But this is not always successful, so be sure you actually want another pet.

Punishing a dog for destructiveness is not effective and may actually make things worse, since it could increase his anxiety.

Severe cases require systematic desensitization to being alone. This can take a long time. Sometimes veterinary prescribed drugs are used as a temporary measure along with the behavior modification program. Because a dog with severe separation anxiety can do damage to himself and/or your home, you may have to figure out some interim measures, such as leaving the dog at a daycare facility, or with a neighbor or family member.

Suggested reading: THE DOG WHO LOVED TOO MUCH by Dr. Nicholas Dodman
I'LL BE HOME SOON by Patricia McConnell PhD.