You're 18 now correct? My advice to you would be to finish up highschool if you haven't already, then get the hell out of his house and start living your own life. You aren't going to be able to change your dad's attitudes towards marijuana over night, if ever. Get your head straight, make a game plan, and get ready for the joys of adulthood. Sure, it can be tough, but take it from me, once you're out of his house and able to control all aspects of your life without him looking over your shoulder, you will be a hell of a lot happier.