From Longman Dictionary of Contemporary Englishstand guard (over somebody/something)stand guard (over somebody/something)XXto watch someone or something so that they do not do anything wrong or so that nothing bad happens to them Soldiers stand guard on street corners. You must stand guard over him at all times. → stand
Examples from the Corpus
stand guard (over somebody/something)• A police officer armed with a semi-automatic gun stood guard.• Riot police stood guard even in tiny back alleys.• Teachers stood guard every night and he was never alone.• Soldiers stand guard on street corners and roam the city at night.• A pro-choice president now stands guard over abortion rights.• Then one stood guard over her while the other two searched the house.• If you stand guard over our stuff, I'll run get the tickets.• A deputy stands guard under the black numeral 2. 