What everyone else has said in this thread. Just drill a hole, depending on the thickness of the stone, 1/4" to 7/8" in diameter, about 4" deep, some 6" deep, and drill two holes in each stone about 2" from the side. The rod, which can be a wooden dowel or rebar should good into the ground at least 6". To some it seems deep, to others not deep enough. I know some who go 12". It's what you want. The stone will stay put barring a hurricane, as we say down here.