If you've been told, or read, that you need to be your dog's 'pack leader', here's a little video to watch --
Here's a good link with a wide range of resources from some very wwidely known dog trainers debunking this theory, for anyone who wants to read more:
Give dogs some credit: I think they are not so stupid as to confuse you, their two-legged, upright, tail-less, non-dog-scented, meal and play and toy and warmth and love-providing human, with a gigantic dog that they must respect as a 'pack leader'. They will indeed respect you if you take the time to train your dog and provide a good social environment for this very social animal-- but for different motivational reasons (and hopefully, never because they fear you).
To prove this point -- just think about your dog and the cats he or she sees. My group of dogs is friendly with my group of cats but clearly never confuses a cat with a dog! Mine don't even confuse 'their' cats with random outdoor cats, who are a temptation to chase (yet they never want to chase another random dog in the same way... or a human). So how could they confuse a human with a dog?
The myth of alpha dogs comes from one specific long ago study about wolves -- which leading wolf researchers now reject!: http://www.4pawsu.com/alphawolf.pdf . The relationships are far more complex.