When Kate barks.... I usually let it go for a bit, just to give people a warning (I don't live in the best area). but if she keeps barking for unnecessary reasons, I usually say in a stern voice "no" or "stop" and I tell her to come by me and sit. That usually gets her stop at the present moment. It doesn't get her to stop all together but I don't really want her to... its not doing any harm in my situation. but in yours, I don't know where you live so it might be bothersome to other people. in that case yu can try spraying him with a water bottle every time he does and hopefully he gets the hint
I find that "SHHHHHHHH!" does the trick. It over powers lots of sounds, including a dogs. If he doesn't stop, go over and gently but assertively go over push him a little to the side with your finger tips. Don't hit the dog of course, but just use your finger tips, this mimicks the mother dog or dominant dogs mouth way of discliplining.