Tested on 3.2.2 ArcEmu Rev 2975.
Requirements;
Deathknight, Mage or Paladin.
What to do:
Start a duel, (Make sure your dueling a spell caster) before the duel starts cast either;
Mage;
Ice Barrier
Mana Shield
Pally;
Sacred Shield
DK;
Anti Magic Shell.
Once the player attacks you and your spell absorbs the damage, if the shield is dispelled by absorbing the damage you will be immune to spell damage until you die by melee or relog.
*This does not work on all of the ArcEmu Revs*