"Hired Sentinel" Ability Idea

[Marauder]

Since Mercenaries are often employed to protect Traders or even people of other guilds, I'd like to see an ability much like Protector's Vow, maybe a bit less effective, for Mercenaries to acquire. Of course, this would passively raise the chance to intercept attacks while guarding someone, thus making the guardian in question just a bit more effective than someone without the ability.

My reasoning for this is because last time I went somewhere with a Mercenary (of pretty immense skill, mind you), my character was nearly killed. Now that would be fine and all if my character wasn't being guarded by a masterful Mercenary in plate armor, I think it was, but it seems kind of pathetic for a member of said guild to have their employer nearly mortally wounded by NPCs that the Mercenary has no trouble with otherwise.