I have thought this was a problem for a while but now think something needs to be said.
If you shield you should still be visible to the general public. This would give people that are not shielded more enemies to choose from, would reduce the need for coordinated shield hoping, increase the amount of points that both shielded and non shielded players get.
I know that some alliances would coordinated to only hit shield players, but this is pretty much already happening anyways.