Slander/Defamation of Character Rights?

I am dealing with a nightmare situation at my work. I have an angry ex-client who has filed a grievance against me through my agency and has sent it to other professionals in the community that I work with. The grievance is filled with slanderous lies (that I can prove are lies, luckily.) This client has made accusations that I coached a child to make false allegations against them. They went so far as to say that I snuck into their bedroom when I thought I was alone in the house, took pictures of a paddle and then showed the pictures to a 6 year old to brainwash into making false allegations against them. This is clearly untrue and I have evidence to prove it. As a social worker, this kind of allegation is a huge threat to my professional career. They continue to lie and share the lies with people I have working relationships with. Any legal recourse on my end?