Incorporeal monsters like ghosts and shades are only hit with blessed objects, artifacts, magical attacks, etc 50% of the time they would have otherwise. The only items that are guaranteed to hit (assuming you make the to-hit roll) are those made of either silver or bone.

Make orcish armor out of bone rather than iron.

Armor made of bone increases your spellcasting ability somehow (many ways to do this; decrease failure rate? Decrease Pw cost?)