Ever since W101 had problems with chain stunning they made the effect after being stunned 1 shield. It wasn't enough to fix the chain stunning problem so they made it 4. This is supposed to be temporary since 4 stun shields makes the meant use of stunning nearly impossible.
My fix to this problem is to put a stun block aura around the opponent for 3 rounds. This aura goes around other auras so you cant get rid of it or use this to get rid of there auras.
This works better because when you have 4 stun shields, it is longer then 4 turns to remove them, (or shorter in some cases). With auras its a fixed amount of time.