From www.ccwatershed.org:
Sáncte Míchael Archángele, defénde nos in proélio, cóntra nequítiam et insídias diáboli ésto præsídium. Ímperet ílli Déus, súpplices deprecámur: tuque, prínceps milítiæ cæléstis, Sátanam aliósque spíritus malígnos, qui ad perditiónem animárum pervagántur in múndo, divína virtúte, in inférnum detrúde. Ámen.
St. Michael the Archangel, defend us in battle, be our protection against the wickedness and snares of the devil. May God rebuke him we humbly pray; and do thou, O Prince of the Heavenly host, by the power of God, cast into hell Satan and all the evil spirits who prowl about the world seeking the ruin of souls.