Ten years before you can bury again

Talked to a Muslim gravedigger the other night. He was a remarkably cheerful chap, considering the soberness of his profession. But I guess Undertakers in the States have that reputation too, sometimes.
(side note: He has his very own Caste).
When Muslims bury the dead, they do not preserve the body in any way, but just wrap it in a simple white sheet, and put it in the ground. No headstone, just a pile of earth. And in a hot and (usually) moist climate such as this one, bodies disintrigate rapidly.
Since space is such a huge premium in the mind-boggelingly crowded alleys of Varanasi, they obviously have to bury on top of a place where someone else was buried before. So I asked him how long would he wait, before he dug a fresh grave on a site where someone was buried previously.
His reply was "Ten years, Doctor-Sahib. I have every space memorized in these graveyards (accounting for thousands of graves), and I know where I can bury someone. If I wait ten years, then there will be no bones or anything when I start digging anew."