Rock Skin is a Prayer that temporarily boosts a player's Defence skill by 4 levels when calculating block chance. It cannot be used in conjunction with any of the other prayers that provide a defence bonus, such as Thick Skin or Steel Skin. This is the second prayer to which players have access that affects defence, and the sixth prayer to which players have access. Once unlocked, Rock Skin replaces Thick Skin. In turn, Rock Skin becomes unavailable after Steel Skin is unlocked.