User blog comment:Willbachbakal/(Champion Concept) Skjold, the Shield Warrior/@comment-5088437-20130119205028/@comment-1330314-20130120065136

I'm not asking to fundamentally change the game's tech, the barrier would just need to check if it's on a trajectory line, whether it be defined by the ability itself (skillshot/dash/homing projectile) or the line linking the caster to the target, both of which can be easily retrieved. And of course you're going to have a hard time protecting your carry if you blow all of your cooldowns. No other champ can protect the carry without their abilities either.

About the barrier's placement, right now it's supposed to be always spawned in front of him, though this may or may not change.