Best way to deal with a sh!t boss?

I received a wonderful letter of recommendation from my director last week thanking me for all my hard work for the organization. This week it's been brought to my attention that my boss that loves to harass me is attempting to smear my reputation by nit-picking every little mistake I ever made. What is the best way I should go about protecting myself aside from documenting all my work? I am also looking for a new job but haven't received any solid offers yet. Thanks