Why dogs bark

The first point is that barking is a form of communication. When a dog barks, there is a reason for it. Sometimes it will be a simple reason when the dogs see someone or something and in other times the dog wants your help. You need to find out why a dog is barking in order to stop them doing it.

When your dog barks all the time he is sending you a distress signal. He needs something what he didn't get so far. Are you walking enough? Is he living a well balanced life? All those questions should come up in your mind.
And don't think a dog will greets you with barking. That's usally a sign that your dog is bored and lonely cause its not a natural setting. Dogs simply don't use emotions like we do. Remember that they are dogs!