“用壕沟围住”可以翻译为 “surround with a trench” 或者 “encircle with a trench” 。
例句：
They decided to surround the important area with a trench to enhance its security. （他们决定用壕沟将重要区域围住，以增强其安全性。）
The castle was encircled with a deep trench to prevent enemies from approaching easily. （城堡周围被一条深深的壕沟围住，以防止敌人轻易靠近 。）