镇守 zhènshǒu
[guard (a strategically important place)] 驻军防守
镇守边关
镇压驻守。 《三国志．卷一六．魏书．杜畿传》：「若以北方当须镇守，自可专置大将以镇安之。」
英语 (of troops stationed in a strategic area) to defend, (fig.) to stand guard, to protect