Well, that's a bit of a problem these days.  We don't have easy access to the kind of equipment Pop had from his 'day job.'  This is not it, but similar.  

They dug 42" holes 20' deep pretty much no matter what got in the way for bases for traffic lights and signals.  Digging a post hole 10' wasn't really any more work then digging one 4' with that truck.  Now filling it back in....that was a different story.   He had a thing for tamping posts, too.  I'm glad I wasn't big enough to do it :)

The fence contractors here are generally capable of 8'.   Less then that just doesn't really work if you want to hold a half mile of fence tight  with the rock and high shrink-swell clay here. 

The family Pop worked for in the lighting business owns a lot of land in the county west of us.  You can tell their land by the fences...... no brace posts anywhere to be seen.