My girls are confined to a run during the work week. I just threw 2-3 handfuls of grit on the run ground and figured they'd scratch at it and get what they needed. They free-range in my yard on the weekend when I'm home.
When they were little I gave them grit in a bowl and you'd think it was chick chocolate, they loved it so much.
My layer feed contains both grit and oyster shell. Every now and then I give the girls some grit (for fun) in a wall-mount feeder. They *love* that. I know they don't need it but the instinct is so strong I prefer to let them play.