I've had chickens for a few years now, and They do a great job of tilling up land and destroying weeds. I lost a few to some predators and a few flew away and got nabbed, so I shrunk up thier run and converted thier old run into a second garden. This is going to double my garden space. I now have two areas to work with, one i can do high rotation quick maturing crops and the other I can do long season crops.
Using chicken to till and fertilize worked great. When I built the coop, I hadn't planned on moving it, and I would have built a chicken tractor if I had to do it over again.