  Let $F$ be a subfield of the algebraic closure of a finite field
$\mathbb{F}_p$, $p \ne 2$, and let $R$ denote any ring such that $F[t] \subset
R \subsetneq F(t)$. Let $G$ be a classical Chevalley group of adjoint type
defined over $R$. We prove that the group $G(R)$ has the $R_{\infty}$-property.
