Rock salt has been the customary way of preserving olives here too as long as I remember Fermi. Preserved olives were a must in every household to have around for the 'fasting periods'. My mother and her younger sister were very strickt on what was permitable to eat during those religious periods. My sister, who is now 83, has been doing the family olive preserving. I have been the 'monkey' on the olive trees to reach the shiny olives. My sister does some with the rock sold to use them for making olive bread, the others pickled in vinegar, my preferred olives, and the other traditional way of selecting fresh green olives, hitting them with a stone, keeping them in water for about 7-10 days, changing the water every day to get rid of the bitterness and then in brine. They are served with lemon, oil, garlic and dried coriander. Last October she taught our London born and bred nephew how to cure his olives.