Is there anything we can do about a gentleman spreading lies about our establishment?

Hello sir or ma'am. My name is Shawn, I work as an area supervisor for a restaurant chain. We had a gentleman claim that there was a piece of skin in his food. He raised such a stink over it that he sent it to get analyzed. We had to call the doctor to find the results. Long story short, the test came back that it was vegetable matter. He is still to this day telling people that he found skin in his meal that he purchased from us. He is also threatening for compensation of the test he had run on the matter. Not that we would, but is there anything we could do about him spreading lies about the situation? Any info would be helpful as he has shown back up 2 years later looking for handouts and telling anyone who will listen about the "skin" he found in his food. Thanks so much for your time.