Arcane Genetic Alchemy

When: Your opponent's Shooting phase or the
Fight phase.
Target: One Adeptus Custodes Infantry unit
from your army (excluding Anathema Psykana)
that was selected as the target of one or more of
that enemy unit's attacks.
Effect: Until the end of the phase, each time
an attack is allocated to a model, subtract 1 from
the Damage characteristic of that attack.