>>775980well other than fire, you can poison it with special stump killer. then bury it back over and hope for the best.
Or wrap a chain around it really well and pull on it with your truck. (use caution with this. if the chain breaks loose and goes flying could seriously hurt something, maybe)
Or keep digging
or all of the above.
Also depends on your end goal, do you want to put something in its place? does it have to be completely removed?
Are you trying to ensure it doesn't grow back in the future?