solid as a rock

(as) solid as a rock

Exceptionally stable, sturdy, and reliable. They've been married for 50 years, so their relationship has to be solid as a rock. That table must be as solid as a rock to withstand the ceiling collapse with hardly a scratch.
See also: rock, solid
Farlex Dictionary of Idioms.

*solid as a rock

Cliché very solid; dependable. (*Also: as ~.) Jean has been lifting weights every day, and her arm muscles are solid as a rock. This company has always built power tools that are as solid as a rock.
See also: rock, solid
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

(as) solid as a ˈrock

extremely solid and reliable: The Irish team were solid as a rock in defence. ▶ ˌrock-ˈsolid adj.: The company has a rock-solid reputation.
See also: rock, solid
Farlex Partner Idioms Dictionary
See also:
  • (as) solid as a rock
  • solid
  • be (as) solid as a rock
  • (as) sound as a dollar
  • sound as a dollar
  • do (one) a solid
  • be (as) sound as a dollar
  • (as) smooth as glass
  • smooth as glass
  • firm up