There are lots of things that might work to nudge away an incoming asteroid, especially if you can get decent advance warning. Once we finally get the cost of reaching orbit down we really should try to alter the orbit of some asteroids whose orbits stay safely sun-ward to us. Assuming the human race plans to stick around for a long time (which eventually requires cheaper trips to orbit) some day we'll need to redirect an incoming rock. I'd rather we didn't have to get it right the first time. Fortunately God has provided some rocks in safe orbits for practice.