Here's a saint you can use. This bishop of Soissons became the patron of champions, invoked against enemy attacks. It was said that if one spent a night in his tomb, one became invincible.
Entire platoons would camp out there overnight before battles.
Of course, Thomas a Becket also visited the tomb before he returned to England, where he was murdered at the altar of Canterbury Cathedral, so you can't put all your faith in a saint's legend.