Other than paasive protection, you can use your shield more agressively. The first 2 second of shield makes a mage the strongest tank in this game, bcs in that 2 sec even a lvl 1 mage with crap gears is more robust than a lvl 66 warrior with nightmare set.
Most mages use shield before forwarding, which is a huge waste. When you see a huge pack of 15+mobs in maus6, mage with late-released shield is the best tank to start attacking bcs no one can scratch you even a hair. Late-release means you charge and hold your shield, walk into mobs, then release it so that the 2 sec can be used when all mobs attacking you. So, all other team members, including warriors will be safe. Isn't that cool?