Your dog does not need you, your roommate, or any visitors to be "alpha."
What he needs is to be well-trained to do the behaviors you want to see, and feel safe enough not to be reactive and aggressive.
There is no such thing as "dog psychology." There is, however, ethology, behaviorism and other serious, scientific studies about dogs, and they all clearly point to the "be the alpha" idea as false.
Really, I'm trying to make your life easier! Check it out:
http://www.kathysdao.com/articles/Forget_About_Being_Alpha_in_Your_Pack.html
http://www.apdt.com.au/files/dominancestatement.pdf
http://www.jeandonaldson.com/jeans-blog-mainmenu-51/64-are-dogs-pack-animals
http://www.nonlineardogs.com/100MostSillyIntro.html
http://www.sciencedaily.com/releases/2009/05/090521112711.htm
http://www.wolf.org/wolves/news/iwmag/2008/winter/alphawolf.pdf
http://www.sciencedaily.com/releases/2009/06/090611065839.htm