Most dogs love to bark, and that can be VERY useful. Actually, this can be worked into a "job", and all Dogs need a job.
I allow my guys to bark rather freely, praising them highly when it's right, and not praising at all, when it's wrong. I think that positive reinforcement is best for me, though,
yorkietalkjilly's is a good way too.
I differ in the "control" issue, by using/repeating the word "Hay" a few times, but, speak it very quietly, actually a whisper. I do this to intentionally keep my voice and presence somewhat undetectable by someone who might be near/outside. I try to impress on them that the word "Hay" is not scolding, just to quiet them down, and usually pet them a little, after they comply. The more an Intruder doesn't know about you, the better, and that includes where you are. My guys respond to several other "whispered" commands as well.
SO many times, people think that a small Dog is useless against an intrusion (territorial or residential). Actually, it doesn't matter how big a dog is, if a Human wants to overcome it, he can. So IMHO there's no use in putting one of our animals in harm's way ever, weather it weights 2 lbs or 200.
What they can do is...
Sleep lightly & patrol regularly,
Use their Eyes, Ears and Noses to detect,
Bark Loudly when they notice something, and
RETREAT (keep their distance) from a Human threat.
If they're wrong, you can work that out later.
