Set ban timer or make ban permanent

We're currently using Dolphin 7.0.6.  When we ban spammers, the ban is regrettably lifted the next day.  Is there a way we can either (a) make the ban permanent or (b) set the timer which controls how long the ban remains in effect.  If we can't do this in dolphin 7.0.6, can we do this in a more recent version of dolphin or a future/planned version of Dolphin???