Here are some tips to stop a dog barking (for additional advice I have put a helpful link at the end):
The most important thing is that your dog must learn that barking for attention won't work
Make sure your dog has the basic things: food and water, comfortable quiet place to relax, and if necessary, bring him indoors.
Sometimes the problem barker has never learned to be alone or is accustomed to lavish attention without having to earn it...
Don't make a big deal out of being gone for a long time, no long goodbyes, dogs will pick up on the emotions and think it's a big deal.
Get creative and give your dog things to do when you are gone
I find devices like the citronella anti bark collars cruel and work for a short time until the dog figures out that when he barks he just has to move his head away from the spray - devices like these say more about the owner than the dog.
If you want some additional help and good basic dog training tips then I suggest you visit Dove's dog training , you will find plenty of great help there.
Hope that helps, all the best!!
Cheers