I use a tarp pinned down with a couple of logs on top of the hutch and the stretched to the ground at a 45 degree angle and pinned down at the ground with a couple of other logs, it allows shade but air can still circulate.
Also in the big run I put a big bowl of water with stones in it, it seems to encourage them to dip their heads under to retrieve the stones. Even the kits enjoy dipping their heads in that.