I was listening to your "awesome shit" podcast this week (while I was plastering the inside of my new straw bale work shed), about well repair issues, and you mentioned something about how the hell your water line was put in such rocky soil.
And, then I remembered I saw this video, about a tool that uses pressurized air to dig trenches in rocky soil, and it really works great (according to the video). Another benefit, is that it does not destroy tree roots. Can you imagine digging a trench, and keeping the tree roots?!!!
It's called an Air Spade, used by arborists for excavating root systems. Hope that helps those looking for rentals.