pour water on a duck's back

pour water on a duck's back

To do or attempt something futile or useless. I know you dislike Reginald's new companion, but I doubt he'll listen if you lecture him. It would be like pouring water on a duck's back.
See also: back, on, pour, water
Farlex Dictionary of Idioms.
See also:
  • have (something) against (someone or something)
  • have against
  • have something against
  • not bear the sight of (someone or something)
  • bring sand to the beach
  • sour on
  • sour on (someone or something)
  • harbor (something) against (someone or something)
  • harbor (something) toward (someone or something)
  • harbor against