What causes a kidney stone and how do you avoid getting one?

The following: Dehydration causes concentrated urine containing xs salts which precipitate & once tiny "kernel" forms more salts come out of solution & stone develops. Can be metabolic causing xs calcium, uric acid etc in urine. Anatomic congenital or acquired obstruction-> "urinary stagnation". Stone can form around mucus or bacterial debris. Prevent by copious water intake, minimal dietary salt or ?Medication.