A robust dynamic controller for delay differential equations is proposed. Robustness refers here to the fact that the exact value of the delay does not need to be known a priori, a situation often assumed in the literature on delay systems, but which is hardly realistic. The design follows the Lyapunov-Krasovskii based methodology and the perturbation analysis based on Rouche's theorem. In addition, we develop a methodology to obtain less conservative stability conditions for systems with commensurate delays, which in turn improves also on the conditions in the general case when combined with the perturbation analysis.