as tough as old boots

Từ điển Oxford Advanced Learner 8th

(as) tough as old ˈboots | (as) tough as ˈnails idiom
(informal)
1. very strong and able to deal successfully with difficult conditions or situations
•She's almost 90 but she's still as tough as old boots.
2. not feeling or showing any emotion
Main entry: ↑tough_idiom