Hmm...
I've heard that when dogs do this its because they believe they are the dominant one in your relationship. To break them of the habit, you're supposed to have a staring contest with them. First one to break eye-contact loses. When my fiance moved in with me, Sabby started marking all of his (my fiance's) stuff. So I told Justin to have a staring contest with Sabby. It seemed to work. If you try it, let me know how it goes.