I agree with "derhannes". That would be the controls I tried first.
Maybe you should implement a maximum angle for bending.
Duke fell through the path as I tried to make a circle. He then fell through the path.
Also he sometimes turns around and walks to the left which is bothersome because you always bend the complete path at the right of the mouse.
I could not figure out when exactly he does turn around.
It would be cool if there where some obstacles that are running on the same path as the duke, so you need to keep them from hitting duke.