steady as a rock

Idioms  

1. Firm, dependable, as in Betty always knows her part; she's steady as a rock. This simile uses rock in the sense of “something that affords a sure support,” a usage dating from the early 1500s.

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Example Sentences

"What a lot of people who don't play darts don't understand is how difficult it is to play. You've got all this adrenaline, all the emotions whirling round inside you and you have to stay as steady as a rock to throw that dart properly at the target."

From BBC

He loves to say he’s steady as a rock.

From Slate

Lillian described The Queen as being "steady as a rock".

From BBC

"Steady as a rock," Lillian replied.

From BBC

He holds me, steady as a rock.

From Literature