Purity: Obligations of Burial
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 602:
It is obligatory to bury a corpse in a manner that its smell does not come out and predatory animals cannot dig it out. If there is a danger that an animal will dig it out, the grave must be strengthened with bricks or similar things.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)