People like to place at the edge of the hole and watch the dirt being moved and it is a big headache for any operator to continue his work. There is actually no reason for them to be there but they stay there due to habit.
People on the ground should place well away from the machine operating area. Keeping this important point at safety meetings, foremen need to implement this, not the operator.
While going to start work, use the horn to warn people to go back; stop the machine if required; and all the time check your back before backing up the machine.