Does the expression, “As sound as a pound” still holds its currency?

Solution 1:

Sound as a pound:

if something is as sound as a pound, it is very good or reliable.

Ngram shows that the expression sound as a pound was popular in the 40s and 50s, but it is less common now.

The expression sound as a dollar, which has always been more popular in US, seems to be the most common expression nowadays.

sound as a dollar: see Ngram

• very secure and dependable. (*Also: as ~.) This investment is as sound as a dollar. I wouldn't put my money in a bank that isn't sound as a dollar.

Source:McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

Solution 2:

As long as we're consulting the nGram oracle, this one suggests that even though the phrase took a beating in the two World Wars and Great Depression, good as gold continues to reflect a popular preference for precious metals over fiat currencies.

Solution 3:

Another phrase that comes to mind is rock solid. Here are its definitions from Collins English Dictionary.

adjective

1. very hard ⇒ "Freeze it until firm but not rock solid."
2. extremely reliable ⇒ "a man of rock-solid integrity" ⇒ "The firm is rock-solid financially."

This appears to be a new phrase. Looking at its use at Google Ngram, it's taken on an exponential growth since 1980.