be secure against assault; be strongly fortified; impregnable/“他媽的，”徐鵬飛突然把開關(guān)一扭，關(guān)上了收音機(jī)：“什么～！連牛皮都不會吹！” (羅廣斌、楊益言《紅巖》596) “Damn them!” Xu Pengfei switched off the radio. “Strong as iron! They can’t even lie properly!”
固若金湯ɡù ruò jīn tānɡ
金：指金城；湯：指湯池。比喻所守的城池或陣地非常牢固。impregnable, strongly fortified, be secure against assault