neb:
MikeAqua:

 

I've used a hired post hole borer to dig holes in compacted hardfill. It was a pendulum style, hydraulically driven machine.

 

That's a really clever design! I've only seen the handheld one/two-person ones which I imagine wouldn't have a hope in hardfill.

 

I hired one to dig a couple of hundred holes at our last place.  The whole section had been built up close to 800mm with compacted fill.  Took a couple of digs per hole, but got it done.