Just read this article on Treehugger.com. What an interesting concept! We've been thinking about getting chickens next year. Do any of you have chickens? Would you implement this? There's a video on the treehugger link. :)
Image credit: Ecofilms Australia
We've already seen how one farmer trains her chickens to eat slugs, and the internet is full of examples of chicken tractors—portable coops that can be moved to allow hens to till, fertilize, and weed a plot while providing pest control in the process. (see also this overview of chicken tractors at Planet Green.) But one Australian permaculturist has taken this idea to the next level—designing an intricate system of "chook tunnels" that let him funnel his ladies into any part of his garden. The amount of work that these creatures can do is actually quite amazing.
To read the article (and see the video): http://www.treehugger.com/files/2011/09/clever-tunnel-chickens-gardening.php