We even had a 'rock picker" to help the gardeners, it dug abut 18 inches deep, dug everything up, the dirt fell through a barred web back to where it came from, the rocks, up 30 to 36 inches, carried on to a side conveyor into a truck.
Worked perfectly, just come back ever third or fourth year to get the next crop of stones.
Stones grow better that weeds, and are harder to get rid off.