the cure is simple - have the police wait undercover for the felons to show up and then arrest them on the spot.
If they actually did this (which they couldn't 'cause it would be voter intimidation, don'tchasee?) there would doubtless be many interesting results. For example it might turn out that some persons turning up to vote in the name of a person weren't that person. Likewise it might be found that someone who had never shown up at the polls at all nevertheless had been striken off the rolls as having voted by the time the votes had been turned in to the counting center.