Not Impossible! Difficult... a little.
You can't plan a picture perfect garden and yard and expect the chickens to abide by the rules you set in place, our chickens cut their own pathes, dig in exposed dirt, scratch for bugs and worms, and poop where they please. (sometimes also laying eggs where they please!) This is how we've done it for the past years-
1. Make Sure Nothing Is Poisonous. For the most part, chickens probably won't eat anything thats bad for them, I don't know why they seem to avoid that stuff, but not planting them will guarantee you'll have no dumb bird eating something they shouldn't!!
2. Designated Chicken Areas. We found that the ladies like a dry, soil area for dust bathes. We also found that once their holes got quite deep, they'd find a new spot in the garden and dig a hole, so we made a small covered area and refill it with a shovel or two of dirt into their bath holes every month or so. They keep using it and enjoying the dry, covered, sunny spot, and we don't have random ditches in the garden beds!
3. Anything YOU want to Eat, they also want to eat. We had to build a HUGE cage around our Raspberries, Blueberries and Strawberries and even then the ladies get in. If you're growing a lot of food for yourself, you're probably going to have to make it chicken proof.
Try not to plant over their paths, they'll just make new ones. We literally put a hole in our garden fence so they could easily walk through so they would stop messing up everywhere else trying to get over the 3' fence! It's worked nicely and their path is small and contained : D
Our yard is a quarter acre or so, and we only really have 12-20 chickens at any given time, getting free full range of the yard every day. The garden (where the coop is) is a little messy, but the main yard with the grass and flowerbeds and such stays fairly good. Here in WA the rains generally wash the poop away in the main yard, and the chickens enjoy a nice grass salad.
