Well, I'm guessing Zeus' shield is already energy resistant, if not impervious. I can make it have an anti projectile feature, it would just be a matter of what eliminates the projectile and how. I propose two options: I use runes and converters to make a "sponge" which can soak up any forms of energy or magic, and use that to take out projectiles. This would be an automatic feature, and I could easily install energy generators as a backup if there is no energy to feed off of. Or I use the "sponge" converter again, but make it so that it reinforces the shield with a layer of all the energy it absorbed.