Winter has started, ground is frozen and covered in snow. My covered run area (underneath coop) is a base of gravel/sand and covered with mulch, leaves and straw to a depth of ~18". My flock has two groups - seven 26 week old pullets and eight 6 week old chicks; the older ones tend to spend their day in the run area, the others tend to stay in the coop. I want to ensure that sufficient grit is available, propose to put clean construction sand in a plastic container strapped to an inside. I have crushed oyster shell in a container strapped to a wall, could mix sand in with that? What is the best way to provide any needed grit for the flock?