I had this same problem with my girl up until today. It got extremely bad since we moved to a new home where our neighbors let their dogs roam free (
). After a while she would bark at anything, including my boy running to play fetch. We finally reached the breaking point and got a bark-collar. Before this whole barking mess I'd be the first hollarin' about how mean it is to use one of these, but it worked immediately. The one we picked is rated for 8lbs+ and she is on the bigger side (probably 9lbs right now). She actually tested it out seeing how much she could bark before the shock really bothered her. After 4 tries, she quit and now we can play outside without the barking driving our neighbors (and landlord!) nuts.
So, if all else fails and the pup is the right weight for it, I would recommend the bark-collar... never thought I would, but it works and fast!