Is this still a dig until you find something or accidentally find something process or is there some "x-ray - sonar-whatever" that can see below the ground?
I remember some cool shops in Montana where you could buy slabs for $20. Awesome for science class
I asked a paleontologist about this recently, and their answer was that the density of fossils is too similar to the surrounding material for ground-penetrating radar to be useful. I wonder whether the challenges couldn't be addressed with the right technology-- maybe borrowing from radio telescopes.
That said, "dig until you find something" is not really the way it's done. You find bits of bone on the surface, or sticking out of a hillside, or anywhere that the earth has recently been weathered away, and look and dig near there.
Edit to add: You, too, can go on a dino dig through Experiment's (YC W13) partnership with https://twitter.com/BBPaleo. I highly recommend it!
I remember some cool shops in Montana where you could buy slabs for $20. Awesome for science class