This phrase is often looked at in two ways: "Who will protect the protectors" and " Who will protect us from the protectors". Obviously, these have two very different meanings. The most used one in fiction seems to be the latter, meaning the people in charge of protecting us tend to gain too much power, and counter measures must be in place should their "protection" grow unpleasant. But the former one is often explored in addition to the latter: who cares for the protectors and gives them what they need and ensures their health and well-being . This dichotomy is on full display in the (partially) Trope Naming Watchmen. The question of whether vigilantes should be trusted unpoliced with such power is brought up, but its also made clear that these same vigilantes, even the most morally reprehensible of them, are people too and in need of care, which they don't receive.