Quick question:

Would it be possible to make one's magical speciality the ability to stop magic? My character's first and foremost a warrior, which would render him very vulnerable to magical attacks unless he had some sort of counter. I was thinking that enlarged vas wein in the brain/head region would allow one to counter/negate the mental attacks of others? (e.g. the ability to stop an enemy spellcaster from rendering you unconscious but not allowing them to control your mind).

This wouldn't stop any physical attacks - a magical blow to the head would still knock him out, and he couldn't counter a great ball of fire hurled at him (other than by running very, very fast) but it would at least stop him from being a plaything of any hostile mages.