Sanctic Will
Codex: Imperial Agents, p. 22
Those who battle the forces of the immaterium must be of purest of soul and will. Such beings are trained to resist psychic assault that accompany the temptations of daemons who seek to corrupt and through their presence, shield their allies.
Your Warlord and any attached unit gain the Stubborn and Indomitable Spirit (2+) special rules.