LOL To get something going in the run you may need to give it a little protection until its established; try putting some chicken wire caps over the plants for a few weeks to limit its exposure to their beaks & feet. It looks like although they are sampling the leaves, the plants may be suffering more from being trampled. The chickens may be more excited about the freshly dug earth, and thus the possibility of bugs than the plants. Scratch up the dirt in some other areas and they may concentrate less around the newly planted mint. Also, are these plants the only greenery in the run? Fortunately, my chickens have run of the entire yard so there are green things aplenty; however I think if all they had was the mint they'd keep sampling/trampling it because it was all they had access too. Of course, that's JMO.