$args=array('menu' => 'Main Navigation', 'submenu' => $currentmenu);
...gets the title of the current page and passes it to the wp_nav_menu function, within the Main Navigation menu, to get that page's submenu.
It works, until there are two pages with the same title. In my site, there are two pages called Services, each located under different parent menus, so the code fails.
How could the above code be modified to work based on the current page's ID number instead of page title? Or is there a better way than that?