What remedy is there for false accusations that defame your character?

I have been wrongly accused as retaliating against a new manager, as well as discrimination of his race and "ageism". I could not retaliate against someone who I didn't know had filed accusations against others in our department...I made statements about the culture of our environment being different than what he was bringing to the table, in an effort to "coach" him and get others to follow his lead...and finally, I DID tell him I had a few years of experience to rely on that he didn't so I was trying to help. This all got twisted into false accusations and now I am being investigated next week at work. I find this disturbing to say the least, how easy it is for him to bring this claim and for personnel to act on it. I am completely innocent of all of these things, however, do wish we had never hired him, based on his lack of knowledge and understanding of rural mental health.