The Mariana Trench has volcanic activity at the bottom of it, which would effectively incinerate zombies (Not really, since they're vents, but anyways...), in addition to the immense water pressure. Considering zombies aren't all too structurally sound, they could probably be crushed by pressure in lesser depths as well.
Originally Posted By: Ephesos
Only one way to deal with zombies.
RETRIBUTION!!!!!!!!!!
But divine retribution only works against living foes...