A problem with using a traditional kinetic impactor in one piece, like the one used by Deep Impact, to deflect a hazardous NEA, is that its effects depend on the subsurface composition of the asteroid.
But what if the impactor consisted of gravel which were released into a stream by a spacecraft in approaching trajectory? The same kinetic energy would be spread out over a larger surface on the asteroid and during a longer time. Shouldn't this prevent fragmentation? And as a bonus also eliminate the risk of hitting a steep topological feature obliquely so that the ejecta flies out sideways.