Pin down what triggers his outbursts; avoid these things for awhile until you have re-established your dominant position (otherwise, you are setting the dog up to fail).

Your dog gets
NO attention unless he is being nice. If you hear a snarl, to the crate in another room he goes...see ya, when you can be *civilized* you can join the rest of us again. I favour zero tolerance for offering to hurt the humans. If you cannot safely get him into his crate, boot him out into the yard, or at least leave the room.

If he knows
the commands "sit" and "lie down", great! If not, teach them ASAP. "Sit" is easily accomplished without even touching the dog, by holding a goodie in front of him and slowly moving it up and towards him until it is above his head. He has to sit in order to to continue staring at the goodie. Say "YES! sit" the INSTANT his rump touches the ground, and praise him/give treats. "Down" is almost as easy--when he's sitting, you drop down and touch the hand containing the treat to the floor. (He will likely drop right down to get the treat...at least, his nose will. ;) This is the beauty of training by utilizing "targeting" methods.) If the rump stays up in the air, maneuver him under a table or something (be creative!) to force him to drop it. If you trust the dog not to bite you, pushing or guiding his rear down into position is also fine.

From now on, he works for EVERYTHING. Food, water, treats, petting, walks, before playing, anything at all he wants or needs from you, he has to do something for YOU first. What he does can be anything you tell him, but "sit" is usually a good standby. Alternate it with "lie down" (a more submissive posture) and other commands just to keep him on his toes. If he ignores you, he doesn't get whatever it is he wants, & that includes his dinner! You can offer it again at a later point if he doesn't sit for it the first time...but don't keep pestering him about it. Offering twice in one day is plenty; going hungry for one night isn't going to kill him, and he'll be that much more eager to sit for you the next day. This is the basic premise of the "Nothing In Life Is Free" or "No Free Lunch" program, and there's plenty of information about it online if you care to read further. :) The whole point is for the dog to understand that he gets *nothing* for nothing--you'll be surprised how eager to please he'll soon become.

The "trick" here is that you--not the dog--are controlling every interaction you have with your dog. It's the first step in taking back your rightful position as the alpha or leader of your family 'pack'. At first, your dog will resent this, and you may see him act out even worse in frustration...but it shouldn't take him too long to accept his demotion. ;) You'll need to pay close attention to how you interact with him, since we do a lot of things every day without even thinking about them. If you are watching TV and he plops his head in your lap, you'll pet him without even thinking about it...if he reminds you he's out of water, you'll fill it immediately...if he does the "peepee dance", you'll race to get the door for him, and you'll let him shoot out ahead of you. No more...From now on, if he comes to you for attention, ignore him until he gives up and goes away...then call him over and pet him briefly if he comes. If he wants to play, wait until he stops pestering you with the toy...then pick it up and play with him (but quit before you think he's ready--this way, you've not only controlled when the game started, but when it stopped as well). This sort of thing may seem silly at first, but it doesn't seem silly to the dog...this is how they think. All those little "power plays" that slip by you unnoticed, never slip by your dog!

Other tips on
gaining and keeping the "alpha" position: the alpha--that's you--eats first...then feed the dog. YOU go thru doors first. If you are walking across the room & the dog is in your way, he moves...you don't go around him! Especially watch those doorways; dominant dogs like to control traffic by lying across them. If you tell him to clear out of the doorway so you can pass, and he doesn't...shuffle your feet and go 'through' him...he'll move. When you come home and want to give him some attention, call the dog to you--don't go to him.  (On the flip side, you go to him when correcting him! Calling a dog to you to be punished quickly teaches them not to come when you call. ;)
Work your way up to 'dominance moves' such as standing or leaning over him, bear-hugging him from above, or rolling him on his back for tummy rubs. These are more confrontational maneuvers, so be sure you are perceived as the alpha or are at least physically able to control him before trying  these positions.
Above all, alpha is an ATTITUDE--feel & act the part. Dogs pick up on subtle cues such as body language. Walk tall & proud around him: be calm, confident, and self-assured. Tell him what he's to do, don't "ask him to pretty please do what mommy says". Be secure in your leadership. There is an excellent link on being the alpha here:
http://www.chowwelfare.com/cciw/alpha.htm  
Be aware that your dog is observing your body language, and he can read you like a book. If you're afraid of him or are not a confident alpha, you can bet he knows it. By the same token, you'll need to pay extremely close attention to the dog's body language and actions as well, and brush up on what each posture means. For example, licking your face, approaching you with head slightly down, wearing sideways "airplane ears", tail held low and perhaps to the side (NOT between the legs, BTW, that's a sign of fear & it has its own set of problems),  averted eyes, and even submissive peeing are good things. Tail held stiffly and high, ears erect, head tall & proud, and any attempt to stand over you or push you out of his way are bad things. Be sure to reward submissive postures and behaviours when you see them!  :)

CONSISTENCY
is a huge factor in turning around a dominant dog. Being unpredictable will undermine his trust in you, and will have him always wondering if you'll bother to enforce it this time, or if he'll be able to get away with one. All family members need to follow the game plan, and do it every time. In a nutshell--hang in there. Sometimes it takes awhile...months...before you see him change his attitude. In the meantime, never give a command you don't plan to enforce. When he shows disrespect for the alpha by growling and threatening, or deliberately ignoring commands you are positive he understands, correct him instantly (if possible) and very briefly, then walk away and ignore him. Timing is everything.

Corrections will vary, depending on the age and size of the dog, how comfortable you are with him, whether you've raised him from a pup, whether you are alpha in his eyes, or still trying to regain that spot...and, of course, your own beliefs and preferences on the topic.
There are a number of
non-physical corrections that are quite effective...and if you have adopted an older dog, or yours has never accepted you as alpha (or you have never physically corrected him before)...then non-physical correction ONLY is highly recommended, at least at this point. Dogs are pack animals, and most of them want nothing more than the company and affections their family. Because of this, "time-outs" spent in a crate are often very effective. If getting him in a crate or out in the yard is not possible in the heat of the moment, simply growl "NO." or "BAD dog." and walk away. This time. However, in the future you may want to consider keeping a leash on him full-time, so the next time this happens you have a means of removing him. The tone of verbal corrections matters: sharp sounds, like "ACK!" or "Aaaah!", and deep,low, grrrowly NO's are usually effective deterrants...and immediately follow with a cheerful, high pitched "gooood puppy!" when he stops whatever bad behaviour he was engaging in. Redirect/distract his attention with an incompatible behaviour whenever possible--for example, if he is chewing the furniture, say "Aaaah!!" or make a sharp noise to distract him, then hand him something appropriate to chew...or, say "NO!", then tell him to sit. (He can't 'sit' and 'eat chair legs' at the same time...) As soon as he stops gnawing the furniture, praise praise praise! Keep in mind that negative attention is still attention, and some dogs will take any attention they can get. In their case, "punishment" can inadvertantly reward the behaviour. Ignoring the dog and walking away is sometimes better. Take note of which method works for your dog.
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