My roommates dog is a prick?

So, you have trained this dog, supposedly, but, I can tell you never proofed it and you have never really corrected the sht out of it for trying to bite invited guests and you. Do it, set it up and put a prong collar on it and correct the living snot out of it if it so much as twitches from a down-stay. Keep doing it til it gets that you are serious. Hope I helped.