Humans you control get +1/+1.
{2}, Tap two untapped Humans you control: Tap target creature an opponent controls.
Because damage remains marked on a creature until the damage is removed as the turn ends, nonlethal damage dealt to a Human you control may become lethal if Sanctuary Lockdown leaves the battlefield during that turn.
Since Sanctuary Lockdown’s activated ability doesn’t have a tap symbol in its cost, you can tap creatures that haven’t been under your control since your most recent turn began to pay the cost.