固若金汤

gāi chéng gù ruò jīn tāng dí rén nán yǐ gōng rù

该城固若金汤，敌人难以攻入。

The city was secured from the enemies.

tā zhè suǒ fáng zi kě yǐ shuō shì gù ruò jīn tāng

她这所房子可以说是固若金汤。

This home of hers is like Fort Knox.

rén rén dōu jué de tā men zhī jiān gù ruò jīn tāng

人人都觉得他们之间固若金汤。

Everybody thought that they were stable.