i like to carry a purge magic...
and if you let him make a creature and a bunch of (currently useless) curses on him without retribution, then you are letting him build up too much. if he had put all that mana into mana crystals, you wouldnt stay in the corner and leave him alone.
now if you are talking about midgame, after you have been walled in, and he starting enchanting a curse flyer, maybe you should break out of that zone. I find walls usually not worth their mana cost