You guys should have a look at a game called life is feudal. In that game you have a monument that is not that different from a shield. You have to feed the monument to keep your claimed land and town protected. If you stop feeding it your radius shrinks and after a time your buildings start to burn down. If you come back and feed the monument you can repair your town. If you dont the town disappears and all you have left is your items on your person. This process takes about 2 weeks. If the player returns they still have some items, if they don't  come back the kingdom has less clutter.