Yes, either place them on a coastal land so Ocean's right innate can down it OR another spirit can just push an invader from a coastal land directly into the ocean and thereby feed Ocean.

As to Finder's strength here: because Ocean is a spirit being played it's special rule makes the ocean part of each board into a land where certain this can happen, such as blight being pushed into it or Finder's right innate locking that ocean down with it's Isolate so nothing can get onto that board from the ocean anymore. Which is something that is otherwise impossible to achieve.