One more point to give you some ideas.
Chickens are jungle creatures at heart, despite all the breeding programs so think jungle when you do your run. It needn't be a plant jungle although it helps. A man made jungle from old pallets, stacked concrete blocks etc, can do the job.
It is a difficult problem.
If you can't cover the top of your run then you need to provide safe havens in the run.
Most runs I see on BYC are completely bare. Large shrubs and bushes are best, but if you can't plant those then making 'tents' out of bamboo, or cane can work. Stake the bottoms of...