Don't simplify integer square roots

Question

How can I rewrite an expression like $\frac{1}{2\sqrt{3}}$ as $\frac{1}{\sqrt{12}}$?

This works in principle, but gets immediately simplified back to the original expression

1/(2 Sqrt[
  3]) /. {Times[Rational[a_, b_], Power[c_, Rational[x_, y_]]] /; 
    x < 0 :> a Power[b^2 c, Rational[x, y]]}