This question is bit specific for Joomla.
I have a main menu consisting of:
Home|About US|Privacy Policy|Portfolio|Contacts US.
Each menu it
The standard way to do it is here: http://docs.joomla.org/Help32:Menus_Menu_Item_Menu_Item_Alias
Just make a second menu with just Privacy Policy & Portfolio in and as a menu item type choose System Links > Menu Alias Item. Then you can choose to link it to the menu item from the menu you created already.
This way you will be able to change the original article link any time and all the alias will update.