Is the marking done above the deceased's body or at the top of the grave, and is sitting on the structure above the grave reprehensible?

Scholars have differed regarding the deepening of the grave. The majority opinion is that it should be deepened to the height of a person or half that, while the Malikis hold that it is preferable not to deepen it. The evidence for the majority is the hadith (definition) reported by Al-Tirmidhi and Ibn Dawud: "Dig, widen, and deepen." As for sitting on a grave or walking on it, both are forbidden. The sanctity of the grave remains as long as the deceased is present in it. If the deceased decomposes, it is permissible to excavate the grave to bury another deceased person in it. The majority also permit its use for agriculture or construction.