My chickens free-range in my backyard. They've got unlimited access to crumbles, dog food (which they steal from the dog) as well as anything they can scrounge up. I also feed them veggie waste (skins, spinach, etc.) There's a lot of dirt available for baths. I was checking out a thread on this group about killing, cleaning & preparing chickens for dinner. One of the photos showed some marble-sized rocks that were taken out of the gizzard. Do I need to make sure they have access to larger rocks, or is eating sandy-soils sufficient?