Updated: Nov 29, 2019
Most dogs bark for a reason.
Contrary to popular belief dogs do not bark to annoy humans, they usually have a good reason. Sometimes they are asking for a dog across the way to come over and play. Many times they are letting others know they do not want them in their area and the intruder should retreat as soon as possible. Terriers were bred to dig underground and to bark excitedly so the hunter could dig to uncover the fox or badger, and also to retrieve their dog. And some dogs just like to hear themselves bark, so maybe they are trying to annoy humans!
If a dog is barking in your presence, yelling, "Shut up!" at the top of your lungs, only conveys to a dog you agree with the barking and are actually joining in. It is best to figure out why they are barking in order to find out if it needs to continue. For instance, most people like their dogs to bark when someone comes to the door but they want them to stop when they realize it is someone they are happy to have at the door. If your dog is left alone all day long they may be barking out of boredom. Since they are outside they are stimulated by many sounds and smells and they are trying to get anyone to come and play with them thus they bark and bark and bark. The best solution for dogs in this situations is to help them with their boredom, like hiding a variety of interesting toys all over the yard. Or keeping them inside to limit their arousal level.
Some humans teach their dogs to speak. Those who have dogs who bark incessantly would wonder why in the world they teach their dogs to do it on cue. Well, that may be the best possible solution for those who have such dogs. When you teach a dog to bark on cue you will also want to simultaneously teach a dog to be quiet on cue. This is a wonderful way of silencing a dog when you need to and giving them the outlet to bark when they need to do so.
No matter what the reason is for a dog's barking it is nice for all concerned to have a way to keep barking to a minimum. So let the dogs bark but please teach them the quiet cue.