My puppy keeps eating bunny poop!!?

My 12 week old Poodle-Yorkie is eating bunny poop every time he is put outside to 'do his business'. He actually looks for it too, he sniffs until he finds the little green pellets. Is there any way to stop him from doing this? Can this be harmful/should I worry?

Update: I forgot to mention, we put up a small 8x6 fence to keep him from finding the bunny poop when he goes, but he is stubborn and refused to go inside of it. Any ideas?
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