Helicopter crashed near NZRA a few years ago. Wreckage rolled on impact into a small gully and lay there inverted.
It took (from memory) about a year to find the wreckage, as the trees & shrubs had closed over the wreckage and the 121.5MHz signal could not escape the metal and soil lying on top of it. This was in a low density populated rural area, not wilderness.
So there you go. ELTs in general, 121.5 or 406, are very useful indeed after a forced landing, but dubious after a serious crash.