how do you kill a guard?

hi all, on my server (aquarius) i see a lot of people killing the city guards and patrol without getting hit by them. i was wondering how people are able to hit the guards and patrol without getting hit back?

Lolz That's when guards get stuck

and now many gaurds get stuck ..xD

They get lured somehow, either attacking a monster or player, away from their post, and they get stuck away from it and don't attack.