At our World Environment Day 2010 permablitz, folks from Transition Kenmore built a chicken tractor.
Chicken tractors come in various shapes, sizes and designs but the essential point is that they are a "movable chicken coop without a floor". This allows the chickens to live outdoors but with some protection from predators. It also allows then to peck, scratch, eat and fertilize the area. Once they are done you can move the tractor to a new area and plant in the newly fertilized space they leave behind.
Here's a few pictures of the chicken tractor we built, based on the book: "The Permaculture Home Garden" by Linda Woodrow. There are of course lots of other possible designs (just do a google search for chicken tractors)