Plants or Rockery for Slopes?

We’ve been fortunate to acquire some land to extend our garden over the past year and amongst it all we have a play tunnel/hill that solved an excess earth problem for us! I planted a few things in in the Autumn but we’ve had a good testing with the rain and, of course, we’ve suffered some land sliding! My question is, would you go with a rockery set up to prevent movement or are there some great plants that will quickly knit it together?