How to deactivate mark?

[Uday S Reddy <uDOTsDOTreddy@cs.bham.ac.uk>]

I tried to define a command called narrow-to-defun as follows:

(defun narrow-to-defun ()
  "Narrow to the current defun around point"
  (interactive)
  (mark-defun)
  (narrow-to-region (point) (mark))
  )

Unfortunately, running the command makes the mark "active," thereby highlighting the defun at the end of the execution.  I have tried various tricks to get the mark to turn off - like calling deactivate-mark, binding deactivate-mark to t locally, binding transient-mark-mode to nil etc.  But none of them is able to turn off the active mark at the end.  

What am I missing?

Cheers,
Uday Reddy