You'd be surprised what tiny little chicken people can achieve. My new tiny girls could dig for England. They leave their older/bigger sisters for dead in the "destructo-skills" department. They turned the yard into a moon landscape in very short time.
If you want a garden, and you want chickens, you have to separate them. Chickens dig. It's what they do. If you give them a bowl of food, they'll dig in the dirt rather than neatly eat out of the bowl. They will dig up anything "dig-uppable", they have no concept as to what is "good stuff" and what is for them. Having big girls and little girls, I think each could wreck a garden with their skills.