That might be the problem then. Water Skin is doing nothing to my MDEF. Regardless of if I have it on or not, when I go into the castle area I only have 50 resistance.Water Shield (?), which you learn in Trademond, buffs it by 10 points I think. There is also a consumable item that can buff MDEF, you can get it from the alchemist in Trademond after the Riverflow crops quest.