I'm so happy you asked before purchasing an anti-bark collar. It shows that you are a loving, caring pet owner! I train using positive reinforcement techniques and I can tell you first hand that these collars (that zap and spray) are far more harmful to your dog that you can possibly believe. The best way to get your dog to stop barking is through counter-conditioning. It's not hard at all, but it will take some time. Most likely your dog is barking because he is stressed. But even if it is because he is super excited and happy, the same training applies.
Here is a forum for positive training
http://positively.com/forum/index.php
Go there and post your situation with your dog and you will get positive, very helpful advice, I promise! The more details you put into your post (dogs age, food fed, daily schedule including meals, exercise and training, exactly what makes him bark when out (people, dogs, squirrels, etc.) the better. Several of the ladies there are positive behaviorists/trainers as a career and they will offer you excellent advice and direction.
And please let me add, I'm sure some folks will respond that they had success with punishment techniques and collars, but trust me, there is a better way that does NOT hurt, scare or stress your beloved dog. Good luck and I know you will find the answers you need on the forum I linked to.
