My best guess on Arrow Fend / Shield Deflection
 

* Any attack with an AoE greater than 0 (0 = a single target) cannot be deflected or fended.
* Spells, unless they have the "physical" flag, are treated just like magical arrows (i.e. they are harder to deflect with shields.)
* Any spell or missile with the "always hits something" flag (which I believe to be between !Inanimates and oSacreds on my spreadsheet) cannot be deflected by shields or blocked by arrow fend.

Thus, fire darts can be arrow fended, but orb lightning cannot. Also worth noting - arrow fend does not block single target buff spells, which tend to have the always-hits flag.

Does this agree with everyone's experience?

Re: My best guess on Arrow Fend / Shield Deflectio
 

I think Arrow Fend definitely affects spells-and it does not seem logical. But this appears consistent to what you posted in the Alpaca thread. Spells like Blade Wind(physical) are stopped by arrow fend, while rain of stones is not.

aoe1 spells are not affected.