Another grit question....

[JRchickchick]

What about screwing a tuna can (that has holes in the bottom for drainage) to a stake and pounding the stake in the ground to the right height?

 

[Malita]

I live in a naturally rocky area - mostly limestone though - and I let my chickens run loose all day. Thus, I assume I don't need to supplement with grit. Is this a good assumption?