A lot of runs are empty because they are a bit on the smallish side and the chickens have eaten every shred of grass they could reach.
I built an over sized run because I was worried about them eating all of the grass, as a result the run is full of grass and some taller plants and the chickens love it. It gives them more to do, it provides shade in the summer, and they always have "new and exciting" places to scratch around for bugs.
I do have a couple of plastic patio chairs and even a step stool in the run and they do love to perch on top of those or hide underneath. They don't like "toys" the way parrots do, but they do like things to climb on and under.
If you are in San Diego you may not have much space which means plants will disappear fast, but you can still be sure they have plenty of sun and shade, along with a nice dust bath area and a few things to sit on or under.
Edited by Sonya9 - 10/22/15 at 1:32pm