Shields: what parameter stands for the ability of bounching?

Hello folks,
When I used the Great Shield of Artorias for the first time I was surpised very positively. With this shield it is such a pleasure to fight in Anor Londo against all the knights or in New Londo against the Dark Wraiths! They are simply not able to perform their combos! After the first hit at this shield they are bounced and I can hit back. I ask myself what parameter it is that does this but could not find any special things in this wiki data dase.
Unfortunately this shield is very heavy.
If I want to use a different shield which parameter do I have to look for to get a shield that so nicely can bounce hits?

Additional question:
Does it make sense to upgrade this shield? because stability is not affected by upgrading and I never use the attack ability of shields.

Many thanks for your help!

Look up the wiki for deflection type. Mostly, all shields heavier than the Eagle Shield (which is the lightest large shield) are heavily deflecting, medium shield do intermediate, and so on. Only exception i know is the iron round shield Shiva is carrying, which is a medium shield with heavy deflection.
And the upgrades on the GSoA are not worth the souls, except when you go for shield bashes.

The iron round shield has amazing deflection. It may be one of the best PVE shields in the game, because it's awesome to be able to deflect a tarus demon's great axe with a medium shield.

^What?

Stand in front of a tarus demon with the iron round shield equipped. Let it hit you with its greataxe and *clank* watch it bounce harmlessly off your new favorite shield.