The thief tried to use a hostage as a 'human shield'. [=the thief hid behind the hostage so the police would not shoot]
Exercise and good nutrition are a 'shield against' disease. [=exercise and good nutrition protect you from disease]
I think she's 'shielded' her child 'from' the real world for too long.
(..) And I'm not yours. You sure seemed like my enemy when you were killing my friends. For years the Night's Watch have sworn an oath to be the shield that guards the realms of men. And for years we've fallen short of that oath. You belong to the realms of men. (..)2015 TvShow: Game of Thrones Title: Kill the Boy Season: 5 Episode 5