be (as) tough as old boots
1. To have physical strength and/or be rarely sick or injured. Marty has played in 500 straight games—he's tough as old boots. Bert is as tough as old boots, so get him to help you move all this furniture!
2. To have a tough, leathery skin (as of meat). This meat is as tough as old boots—I can't even cut it!
3. To not feel or show one's emotions. Our aunt is as tough as old boots, so we asked her to give the eulogy, knowing that she's the only one who could do it without crying.
4. To be determined, perhaps stubbornly so. You'll never get Rich to change his opinion—he's as tough as old boots.