T.S.
I TOTALLY SYMPATHIZE!! I have teeth marks as we speak. My son is 13 months... and is doing much the same, especially when he is frustrated or tired. I have caught myself even flinching when he comes around, waiting for the clinch of his sharp teeth.
My advice, and it seems to have worked for the most part... I keep a close eye... when he looks like he is about to bite... I place my whole hand over his mouth (this way he cannot get a grasp on anything) and tell him no biting... I hold it there for a second or two, while he tries to get away for another bite. Soon after this, he loses interest and finds a toy.
Good luck! It is a long painful road!