My six month old, Oscar, is starting to go through an independent stage. To establish myself as the alpha one of the things I do is hold him down on his back (on the carpet) for about 30 seconds. I don't let him get up until he relaxes. After several days of doing this he is being more accepting of it. I also make him wait to go through a door until I've gone first. It sounds like your puppy is trying to be the alpha.
