Watch over, act as a lookout, as in We'll climb the tree and get the apples if Josh will stand guard, or There's a parking space; stand guard while I make a U-turn and get to it. This term alludes to the military defense of posting guards to watch for the enemy.
mount/stand/keep ˈguard (over somebody/something)act as a guard: Two soldiers stood guard over the captured weapons.
1. To keep watch.
2. To act as a sentinel.