Here's what worked for Rowdy. He started barking at us at about 3-4 months old when he wanted us to play with him or wanted us to do something for him, or just wanted our attention. I really didn't know what to do so I thought that I would do what his (canine) mom might do if he misbehaved. He was wearing his harness and when he stated the barking at me - I picked him up by the back of his harness and shook him (gently) like his canine mom might do (pick him up by the scruff of the neck or nip him). It startled him so much. He ran to my husband and looked back at me like, "she is crazy!!!"
We only had to do the correction 2 more times and he completely stopped the barking at us to get our attention. I didn't correct him for barking at noises outside and he didn't/doesn't bark when he is playing. Now he barks at the black lab next door and I can't seem to stop it - except when I go outside or look outside, he stops and comes back in the house. I wish I could stop him from starting the barking at the lab - but he only barks when the lab barks, so I guess it could be worse.