First of all I'm shocked he's barking so young, are you sure it's a bark, and not a whine? The way coins in a can works, is that the noise has to be slightly aversive, and loud enough to get their attention. Your voice should be calm. You say "No" or "Uh-uh" in a moderate but stern voice, and shake the can. If he barks again, you repeat, you keep repeating until you have the last shake. I had to use a Christmas tin with Joey; it made a louder noise than a soda can. If he even sees the can now he stops barking. Remember barking is a wired in trait, and you will never stop it completely, they will bark at strangers or noises, but they can learn to stop after a few barks. You must be dedicated to teach this and very consistent. It can't be haphazard where he wins some of the time, or else you actually are reinforcing him to bark. Some people us a water spray bottle, but I like the coins in a can better, because both the stimulus are similar, both are noises and can easily be learned by cause and effect. When I say easily I don't mean one trial learning, this takes weeks and months of practice. I had a can available in every room. Joey is allowed to bark at certain things, and if he sees a dog in the park, he has learned to ring a bell and I will open the door and he can run outside to bark at the intruder, so instead of barking now I hear this little "ring".
