I agree that you try either a spray bottle or a bottle filled with coins/gravel.

Shock collars are definitely not the way to go. My uncle used to have a dog that barked like mad at anything and everything - he eventually gave up and put a shock collar on him. The dog learned that whenever the shock collar was on, don't bark. But AS SOON as the collar was off he'd go mad barking. Collars are not a good way to solve the problem, it's just a temporary fix at best.