The shielding is really just two plates slightly apart from each other. When the debris strikes the first plate it vaporizes and the second plate catches the vapor. It’s called a whipple shield. That first plate prevents back splash when it strikes the second plate. This minimizes debris going back to space.

Graveyard orbits are for geostationary satellites. That are farther out, if I remember correctly, than the standard GEO orbits. Those are premium orbits. They are tightly regulated. Unfortunately, those are way to far out to deorbit on their own. It’s something like a millennia or more before perturbations could cause it to deorbit. Going out to gather them and bring them back is a waste of current resources, hence the graveyard orbit.

If you’re looking to take some real life Aerospace knowledge into kerbal. I recommend searching for “patched conics”. This matches how kerbal models their system and will allow you to understand how they get to their dV calculations plus do slingshots in the game.

You’re in luck too, one of my favorite channels just dropped a video on space debris and debris shields here: https://youtu.be/_FFNz2q7F88

Source: https://ai-solutions.com/_freeflyeruniversityguide/patched_conics_transfer.htm