can of worms vs on the skids

can of worms

noun
  • A complex, troublesome situation arising when a decision or action produces considerable subsequent problems. 

  • A troublesome situation; an issue whose resolution is difficult or contentious but not necessarily complex. 

  • Used other than figuratively or idiomatically: see can, worm. 

on the skids

prep
  • In decline; going downhill; in trouble. 

How often have the words can of worms and on the skids occurred in a corpus of books? (source: Google Ngram Viewer )