Rant: Our Future Generations :]

[hoho]

one more high-explosive missle to detonate slightly closer to the defending ship so the force would push back, slow, or even stop any debris or shrapnel to the point where conventional shielding would hold up.

This doesn't work without atmosphere. Pretty much the only thing that could counter such a "flack missile" is nuke that simply burns up all the debris and sharpnel. Good luck detonating it accurately enough when stuff flies around at several km/s.

Then again you'd likely screw yourself more with the EM blast the nuke causes