I think what you need or want to do for dust baths sometimes depends on where you live. I always have one dust bath in a covered area of the run. We get a lot of rain here and have heavy clay. It makes the dust baths they scratch up on their own useless for a time. It can be weeks before they dry out, during the rainy periods. My birds are exposed to mites from birds migrating to the area in early spring. Then need their dust baths the most, right when the weather is the wettest and their dust baths are the most useless. So for me, giving them a covered dust bath has allowed them to keep mites from getting out of hand. Before that, I had to treat them for mites in the spring.
Since clay tends to hold water and not drain well, I like to add sand to a couple of their dust baths, to loosen it up. One of them also has a lot of peat moss in it. I gave them this the year they became obsessed with a flower bed that had a lot of peat in it. I also add DE to their dust baths. Or at least their main one. Plain wood ash is a great additive, too.
