Erudite: Ward of GlyphsFollow

To all the Erudites out there ... I rolled a Erudite and got Ward of Glyphs. When you get hit it is supposed to take of x amount of damage, right? Well I did some dueling with a friend and maybe I am mistaken but it did not work everytime. I know it only lasts like 20 sec or something. But even if I get hit more than once it is supposed to work right? (as in 3 different creatures hit me it is supposed to take x amount off each hit/ or / while dueling getting hit more than once even by the same character it is supposed to take off x damage from each hit) is this correct or am I mistaken? Any imput would be appreciated. Thanks for your help.