I have drilled various types of boulders and concrete by using a simple tip:

Get a spray bottle, fill it with plain water, and set the nozzle to a solid
stream.

NOTE FOR THE FOLLOWING: For safety, use a cordless drill or a GFI protected
circuit for a corded drill.

Start drilling with a regular masonary bit while an assistant carefully sprays
water at the tip of the drill bit . It goes through like butter. I was amazed
the first time I did this and haven't had to replace a masonary bit since!

RR