Shiny new coop, ground cover suggestion?

[5Chances]

Below are shots of my run. As you can see, they also have access to a large fenced in pen. So they spend most of their fair weather time in the pen but do loiter on the branches at the back of the run in the mornings after breakfast.
This set up has been running for 6 years and I've never removed anything from the run. I just add a trailer load of free wood chips as needed. There is no smell from the run.
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Thank you for sharing! I went with a natural mulch, much like what you have. I am happy with my choice so far!