** unwind-protect with narrowing
   :PROPERTIES:
   :DATE:     2010-06-07
   :END:

I'm not in the subtree

*** I'm in the subtree
    :PROPERTIES:
    :DATE:     2010-06-07
    :END:
#+begin_src emacs-lisp
  (+ 6 "I'm not a number!!")
#+end_src