I'd say this was due mostly to his age (21-22) and sporadic usage patterns as a Rule V pick. As he's matured, his walk rate has come down steadily. Of course, one could argue that Marmol, as a converted catcher, is still learning to be more consistent with his release point, and could develop the control that Santana has. The idea is intriguing, and if I were the Cubs, I might revisit it during spring training next year.