remain under sth meaning

[American slang]
to continue to stay beneath the surface of something.
  Please remain under the umbrella so you don't get wet.
  A lot of people decided to leave the shelter, but I remained under it.

• remain on sth:    [American slang]Go ...
• remain ahead of sth:    [American slang]Go ...
• remain behind so or sth:    [American slang]Go ...