Separation Anxiety is one of the most common complaints of dog owners, although some don't even realize it. What they do notice, is that they often come to destroyed objects and neighbors complaining about the howling and barking.
Dogs are pack animals, and and don't like to be left alone. Some dogs will simply sigh and wait patiently for you to come back, and others will go into panic mode, crying and barking, trying to get you to come back. Some destroy things, such as plants, books, pillows, anything that was "yours", even to the extent of defecating on the floor.
Severely dependant dogs, also known as "velcro dogs", and dogs who have either been passed around from home to home, or have been abandoned are more likely to have Separation Anxiety than others. The thought of being abandoned again, that you are not coming back is a very scary thing. And unfortunately, most owners unwittingly reinforce this anxiety, by making a production of leaving, saying "it will be okay", and trying to reassure the dog has the opposite effect. Nothing enforces a dog's belief that he has something to worry about more than somebody trying to keep him calm.
Like all fears, desensitizing your dog your comings and goings will help him get over his fear of abandonment. Leave the house for a little while, just a few seconds, and then come back. Once your dog is accustomed to seeing you go out and come right back in, you can increase the time you are out.
Exercise will also help in the area. A tired dog will sleep (hopefully) while you are gone, and by wearing him out before you leave, he may be too tired to work up to a good panic.
You may also want to invest in some good, mind-consuming dog toys. A Kong stuffed with cheese or peanut butter is a terrific idea and will keep your dog busy trying to get the goodies out.
Crate-Training has been used with great success in curbing Separation Anxiety. Most dogs prefer small, cozy places to wide open areas, as the closeness is comforting. A crate trained dog will always be safe and comfortable in his crate when you are out of the house.

