Is it 3.0 or 3.5? OA was updated in Dragon #318, IIRC.
I'm thinking about a nezumi sohei... A guardian and protector of the places sacred to its kind. If that doesn't fit the setting (I saw nothing about the ratfolk, except that they're a valid race), then a human sohei instead. (I like the sohei class, they're my fav. OA class.)