A fortress can be fortified to defend against attacks.

要塞可以加强防御以抵抗进攻。

The soldiers are fighting bravely to defend their country from enemy attacks.

士兵们勇敢地战斗以保卫他们的国家免受敌人的攻击。

We need to build a strong defense system to defend against cyber threats.

我们需要建立一个强大的防御系统来抵御网络威胁。

The city walls were built to defend against invasions.

城墙被建造来抵御入侵。

They are learning self-defense techniques to defend against potential threats.

他们正在学习自卫技巧以应对潜在的威胁。

这些造句展示了"defend against"在不同情境下的应用，从物理防御到网络安全防御。希望这些例子对你有所帮助。