N. Korea made some adjustment so that, IIRC, in their third rocket launch, booster rockets were rigged to explode after they were spent. S. Korean military authorities announced at the time that their recovery attempts failed in essence because the rocket was disintegrated into small parts and spread over wide area. They did recover some parts which were intact, though they appeared to be part of outer frame with no components inside.
Thanks Tiger - I was sure you'd have interesting insights on this one...