Perhaps an area-specific "reputation" could help? Every time you get accosted by a guard, your reputation gets worse. Mechanically, this could be represented as the DC of any subsequent persuasion check increasing by 1 and the gold required to bribe increases by X% (multiplicatively, so the bribe price goes up exponentially). I'd also suggest that your area-reputation affects stealth/sleight-of-hand DCs as people and merchants are now more wary of you.
And money paid as bribes should be lost forever.
