The best offense (20G)

Countered enemy attacks 20 times using Shield.

A counter can be performed against nearly any attack and will reflect rockets or melee attacks which will cause recoil damage to the target. To perform a Counter press the 'RB' just before getting hit and you will notice Heller bash the attack enemy back. There is no delay between hitting the button and the shields coming up so with practice you can pretty much counter everything.

Note: For this achievement you must counter melee attacks.