Multiple application folder in CI

I am doing it like this:
application/* for controllers front
application/admin/* for controllers for admin panel

I would also extend the controllers from a "core" controller. eg. Dashboard extends Admin_controller.
Admin_controller here would extend from MY_Controller. This way I can easily build things like access control for different areas of the applications.

So in the application/core folder, I have something like this:
MY_Controller.php
Front_Controller.php (extends MY_Controller)
Admin_Controller.php (extends MY_Controller)