1. Chicken wire is your friend
By making a collar of chicken wire around small plants, you will discourage most of the chickens, if the have enough to eat elsewhere. To give the wire some structure, use tomato cages or a couple of stakes.
When you have a lot of plants, like Bloom, your garden become a bit steampunk in the spring, but at least the chicken wont destroy your plants. This wont stop a determined chicken but there are more defensive tricks to come
6. Plants just for the chickens
When you can't defeat them, work with them. Even chickens need shelter from time to time, and if it's just on hot days to escape from the sun. Planting low growing bushes or evergreen will give your chickens the opportunity to hide and they will use it.