I'm fairly new to this, so if I'm babbling or not making any sense, just ignore me.
Recently, I started the process of joining a local coven, where the Assistant HP is very talented in shielding, or more specifically, shield-breaking. She can tell what visualization is being used to make the shield, and then find the "chinks" in the armor, but when she looks at me, all she can see is "static".
I haven't had the chance (unfortunately) to work with her too much more yet on this, but what I've come to understand about myself and my shield is this: On top of whatever shield you normally use, try to visualize something related, not to block, defend, or even reflect, but rather to misdirection. Similar to Eastern Martial arts, it's the whole idea of "can't hit me if I'm not there". My visualization is usually a combination of (geek alert) a Star Trek-like cloaking field combined with a muted hard plastic (think waterproof-type material).
This doesn't necessarily work when something is actively trying to get through your shield, but the purpose here is to keep them from finding you in the first place to even attack.
Just my $0.02. I'll go sit in the corner now.