Restricted custom menu

Hi,

I have a module with a menu within the slide master.  I would like to restrict access to the menu until the user has completed or viewed the last slide in the module.

I have created a true/false variable for the menu button which is defaulted to false. On the final slide of the module i have created a trigger to change the variable to false and so the users can then see the menu.

My problem is that when the user navigates to another slide from the menu once it can be seen, the menu is then disabled again.

Anyone got any ideas?

Thanks :)