Be (as) sound as a dollar idiom
If something is (as) sound as a dollar, it is very secure, very firm or can be trusted.
She told me that the investment was as sound as a dollar. I'm glad I did not trust her because she lost everything.
This fire alarm is sound as a dollar. It goes off every time it detects smoke.
The cottage is old but it's still as sound as a dollar.
Unchanged, be stable.
With absolute certainty; decisively
Protect one from harm caused by unforeseen events
To indicate refusing to change one's actions or belief about something in spite of criticism.
The verb "be" should be conjugated according to its tense.
This idiom is believed to have become popular when the American dollar was still a secure and dependable currency of the world. However, the global economic circumstances changed and rendered it less strong.
A legal matter that is very easy to solve
The house owners didn't lock the doors before going out, and that's why they got broken in. This is an open and shut case.