Who said that chickens ruin your lawn?
Well, they can ruin it. But check out my friend's lawn - the grass in the chicken run is obviously healthier than the mown part. Her secret is having a big enough area for them to roam around and forage without decimating the grass. Our section has too little lawn and too much garden for that.
I also like the approach of the permaculture blogger at ecothriftylife.wordpress.com - he has a chicken tractor which he moves very regularly around the lawn, so they mow and fertilise it for him.
Do you successfully keep your chickens on a healthy lawn?