Self-fertilizing Chicken Run/Garden???

Hi everyone...this is my first time posting on the forum, and may I just say - this is a GREAT forum and one of my two absolute favorites, with the other being backyardchickens.com! I'm just getting started with SFG and I'm in my first year of raising chickens. When we were getting ready to build our coop/run last summer, I came upon this article about a chicken run/garden:
http://www.backwoodshome.com/articles/silveira44a.html
and so we built our coop with two fenced runs - one on the east and one on the west, with chicken doors on both sides, so they can be in whichever run I choose to let them into. The plan is to have the chickens on one side with the garden on the other side and then in the fall when the garden is done, move them in there to clean it up and fertilize, and just keep moving them from side to side every fall. We went with this plan before I found out about SFG....

Here are some thoughts/questions...
1. Do you think the chickens will compact the Mel's Mix too much and/or will they scratch all the nice loose soil out trying to dust bathe in it? Would leaving the grids on the boxes possibly help?
2. I'm thinking I could plant fast-growing things (suggestions welcomed) in the SFG boxes in the run where the chickens are each spring/summer and just keep it covered with netting until it's well-established and then remove the barrier, providing them with their own little salad bar javascript:emoticonp(':idea:')...so far I have four 4'x4's in each run and the run itself is 24'x24'. The "aisles" between the boxes are going to be covered with coarse sand.
3. My other option (which would kind of defeat the purpose of building this dual-purpose run/garden) would be to cover the boxes with plywood covers when the chickens are in there.

Any thoughts and suggestions would be most appreciated!

By the way, I'm in south-central NE!

Thanks for reading....
Brenda