Short of substantial use of strategic nuclear weapons, nothing Earth has would stop them.
And that assumes that the Custodes start unarmed and naked. Give them their full armory to draw upon and a hundred Custodes would have the entire planet conquered in very short order.
And that assumes that the Custodes start unarmed and naked. Give them their full armory to draw upon and a hundred Custodes would have the entire planet conquered in very short order.