Sanctum of Eternity

A colorless source that doubles as a panic button for exactly one permanent: the commander in the zone that matters. It answers targeted removal, edicts, and exile-if-it-would-die effects by pulling the commander back to hand before the answer resolves, and it reloads enters-the-battlefield triggers on a general built around them. Note what the bounce actually does to the command tax: nothing. Once your commander is in hand you can recast it without paying the tax for that cast, but the moment it heads back to the command zone the counter is right where you left it. Two restrictions do the balancing work. It only touches a commander (nothing else you own qualifies), and it works only during your own turn, so it cannot save the general from a removal spell cast on an opponent's turn. Within your turn, though, it is an instant-speed dodge that stays online through your end step: hold the mana, activate in response to a targeted spell, bounce the commander out of range before that spell resolves. The turn restriction is the real cost, since many of the threats you most want to duck arrive when the ability is offline. As a land, it slots into any base without a color commitment, which is why it shows up so widely despite the narrow effect: the price of running it is close to nothing.