Those only apply to the armor you are wearing, not shields. The thread title specifically says shields.
Arcane Armor Training (Costs a swift action)
Alternatively, get that sucker made of mithril :P
With Arcane Armor Training under dispute at all, you should not really rely on it in many games. If your GM rules that it works with shields, great. Otherwise, you might have to do without. Your only other option is, as it has been said, to get shields with an arcane failure chance of 0. But that is not always practical (what, you expect every smith in the land to be fully stocked on mithril?)
I must admit, I think this is a core advantage of Bards. It allows them better AC than even the magus class because of it (a +2 armor and +2 shield cost less than a +3 armor, so they are easier to acquire) Well, of course only arcane duelists gain the medium and heavy armors to compare.
