Well, good luck with finding anything underground! A horse can find it and hurt itself on it, but when we go to look for the cause of injury, theres nothing in sight!
I would first try and find another cause for his injury before you start digging holes out there. If you walk around the pasture and nothing is visibly poking out of the ground, I wouldn't dig.
Unless you plow the entire field, you won't really know whats under the ground.
And those who were seen dancing were thought to be insane by those who could not hear the music