My Snickers is a barker whenever anyone comes to the door and basically doesn't stop until they leave. It's become a real problem when company comes over! We've been trying the "Dog Whisperer's" method of placing the dog down in a submissive position and holding him there until he calms down. Then reinforcing the 'no bark' verbal command. This has been working in small steps, but he will usually resume barking eventually. I think it's an ongoing process but maybe worth a try.
(I feel your pain..lol)