Bulwark

[Cabalabob]

Bulwark is an additive 60% block rate increase, coupled with your natural block rate so if you had a 20% block rate and used bulwark you'd have 80%. If you have a tower shield you'll notice you block less than with a kite shield during bulwark because of its naturally lower block rate, but each block mitigates more.

Never use bulwark alone for a tank buster, couple it with a proper cd, even a minor one like foresight or Shelton.

You only block or parry when facing an enemy so anything behind or on your flank won't be blocked, locking on to an enemy helps make sure you're always facing them.

You also cannot block or parry while casting, so if you're using stoneskin or clemency during bulwark you're negating the effect.

Finally you can't block magic attacks, so if the tank buster is magical or the trash pull is magic only (like elementals) then bulwark or any cooldown to do with block/parry is redundant.