"a sacred bullet fired into the coffin kill him so that he be true dead"
Bullet
Creative Commons AttributionBullet - Credit: An Nguyen/Wikimedia Commons

In Romania, the precautionary measure of shooting a bullet through the coffin of the recently deceased might be taken. Presumably a sacred bullet is one that has been blessed by a clergyman.

The use of bullets (specifically silver ones) is more common in werewolf fiction.