Barking

The only thing I can suggest is in the split second he does stop barking when told to is to give him praises and a treat. Hopefully in the long run he will come to understand when you say Knock it off, or that's enough, what ever phrases you use he will stop when told to do so. I always do the short "CH" noise when they have gone too far. That alone gets their attention.
I know someone else that is more qualified will come along with the right answer. Good luck and welcome to the forum.

Dogs wont stop barking if you yell at them.  They'll just think you're joining in and bark even more. 

The most important thing is to praise your dog when he does stop barking.  I've had success with a shaker can.  Simply fill an empty coke can with some pennies and duct tape it close.  Shake it once as hard as you can while saying "QUIET" when your dog is barking.  It's better if your dog doesn't see you shaking the can, so try to hide it from his view.  He'll be momentarily surprised.  This is when you praise him lavishly, verbally and with treats.  This trick might work once or twice, but if you overuse it, your dog will just get used to the can and ignore that too.

You can also distract your dog by pulling him away from whatever he's barking at and giving him a string of commands like come, sit, down, stand, etc, etc.  With my dog, I would tell him to be quiet when he barks, praise him, then pull him to the other side of the house and play some fetch with him.

This whole process will be by no means quick.  I've worked on "quiet" with my dog for more than 3 months before he really started listening.  Good luck!

My dog is one of the "barky" breeds.  I was well on the way to teaching him to "speak" on command before I thought about it.  I realized that NOT rewarding barking at any time was a better way to teach him to stay quiet.  That said, there are times when I just want to get him debarked like most of the PHs I know.  He won't be, never fear.  But I do "quiet" and it works some of the time.  Of course when he's being quiet there's lots and lots of praise.

Rewarding when he stops is always going to work better than trying to punish with the bark.   The hardest part is timing the reward to make sure he associates it with stopping the bark rather than with the bark.   Takes some time but it is achievable.

Clyde

Thanks for all the responses to our barking problem. I have to tell you what happened yesterday. Dugan was barking at something outside(typical) when I snapped a rubber band on my wrist in front of him. Boy, did it startle him and made him stop barking immediately. When I snapped it I said "no bark" and when he was quiet, I praised him and gave him a treat. I tried it a few more times last night with the same success. He seems very frightened by the sound but at least I'm not inflicting any physical discomfort. Has anybody  heard of this method before?
In fact, I let Dugan out around 1:00 a.m. when he heard something and started to growl. All I had to say was SNAP and he became quiet. What do you think?

We have been working on quiet for some time with Loki. We have a 6 ft wood fence, so he can't see out of the yard. He pretty much only barks when another dog is walking by. He love to be outside, so we started going outside, telling him to be quiet and praising him if he was. If he was not quiet, we would bring him inside. Now when he barks and we walk outside, he will sit down and look ashamed, then run inside. We never touched him, so it's not a matter of dominance. He just knows we mean business.
 
I do wish that we could stop him from wanting to bark at the dogs walking by though. Also we have a dog that just moved in next door. Sometimes our neighbors have her chained up outside in the yard. Most of the time, Loki and she are fine being out together (again they can't see each other, just smell), but sometimes they will start viciously barking and attacking the fence. I go out and tell him "leave it" and "quiet", but we haven't had luck getting that to stop yet.

What your dog is doing is called "fence fighting"... I have a wooden stockade fence around my yard and my one JRT is trying to chew his way through it to get to the two dogs next door.  He runs up and down the fence barking and they fight through the fence. If anyone knows a way to stop this behavior, please let me know too!  As it is, I only let him run loose in the yard when the other dogs are inside. These crazy dogs!!!