Like, for example, you have a limit of +/- n net Karma you can award to any given poster in an arbitrary time limit t.
That can be also implemented more softly by still allowing anyone to vote anyone as much as they want, but requiring a captcha for each vote after a given limit.
That can be also implemented more softly by still allowing anyone to vote anyone as much as they want, but requiring a captcha for each vote after a given limit.