Okay, as my chicks have been growing, we have been putting potting soil in boxes for them to take "baths" in. They love it. But on Friday we will be putting up the coop and run, and I was wondering what kind of dirt is actually best for them? I've seen regular dirt, potting soil, even sand. I'm not going to make the whole run dirt, just a section. I want them to have access to grass too. So, what dirt is the best to use? And for those who do use sand, what kind of sand do you use? Sand box sand? I just want to do everything right. Thanks!