Rel
Liquid Awesome
Much easier is to make the guard a Minion with regards to non-lethal damage. Successful stealth check + successful hit = unconscious guard.
This is sort of my take as well to an extent. I could easily foresee three flavors of guard, two of which are already supported by the rules.
The first is the total mook guard. He's a minion. This is the guy who guards the guardpost that nobody ever tries to get past. He's barely above the peasant militia.
The second is part of the Royal Guard. He's a soldier and a good one. He's seen more than one battle and he knows that he is part of an elite unit that stands between the King and those that would try and do him harm. Even if taken unawares (unlikely given his good Perception) he won't go down without a fight.
The third is the middle ground (and unsupported by the rules but easy enough to implement). He's a soldier and has been trained. But he's not a hardened veteran. He'll keep a sharp eye out but if taken by surprise he may fall dead or unconscious without a sound. So he's treated as a Minion during the Surprise round and after that he's a regular Soldier.