Game Mechanics - Protection

[NTJedi]

Zylithan said:
quick protection question: If there is a unit with 12 protection, and he gets hit three times in the same round with hits that each do 10 damage.

Does the protection mean he takes no damage, or does it wear down, and he takes 18 out of 30, having blocked 12.

basically, is protection per round or per attack.

thanks!

(ps apologies if this is in the manual, i looked, but didnt find it)

protection is only less effective when the unit has fatique.