Usage patterns
見張りをするto keep watch/lookout
He was keeping watch at the entrance.
見張りに立つto stand guard/on watch
The soldiers took turns standing watch.
見張りを置くto post a lookout/guard
The company posted a guard in front of the warehouse.
〈人〉に見張りを頼むto ask someone to keep watch
I asked a friend to keep watch for me.