If your could plant mulberry trees in their runs... starting with young trees you'd have to fence them off til they got big enough. Then the mulberries could be for your birds. Shake a few branches and the fruit falls to t he ground for them. I've read where one person planted tomatoes to climb on the wire of the run and the chickens get all those tomatoes. Comfrey is good for them but it couldn't be in the run as they would decimate it.
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Sounds like you have a working plan. Hope it goes well for you.
Yes. The best way is to plant whatever on the other side of the run fence. That way they can get part of it through the fence but not destroy the whole plant. Comfrey, tomatoes, whatever. And of course the fruit trees can be in the run and unprotected once they're big enough and established.