I had a dog that thought she was the top dog from the day I brought her home as a pup.  It didn't occur to me that she was asserting herself as the alpha until one day when she went after the two neighbor's dogs (they were much bigger than she) and they took her down by her neck.  All my commands were ignored as my dog raced to defend her territority.

From then on I asserted myself over her.  Eventually my "STOP" would stop her dead in her tracks. 

I had to learn gentle training methods because when I was close to her and was disciplining her, she'd get so excited that she'd wag her tail and pee.....and spray us all.  lol 

Here are a few sites on Becoming the Alpha

http://www.canismajor.com/dog/alpha1.html

http://www.pets.ca/articles/article-alphadog.htm

http://www.google.com/search?hl=en&q=dogs+alpha+training  (googled)