Wiktionary
a. (context simile English) Extremely reliable
Usage examples of "steady as a rock".
The old man was steady as a rock, of course, and those eyes were like bayonets under the dark brows, but the Colonel knew him well enough to guess that he had a full quart of Dimple Haig in his belly, and that something was troubling him deeply.
She was as steady as a rock, leaving the comforting words he intended to say sitting awkwardly on his tongue.
His hands were still shaking a bit as he tore it open, but by the time he was done with his face, he was steady as a rock.
He had even hardened up the independent suspension on the two front wheels, and as the car had stiff suspension at the back, it took comers steady as a rock, leaving other drivers rolling wildly on their cushion springs if they tried to keep up with him.