David Brin, whom I debated on the topic of Transparency yesterday, has been putting forward for some time the general idea of a henchman's amnesty law. Namely that, in the event of a criminal conspiracy, the first underling who whistle-blows can get some level of amnesty, witness protection and/or cash reward. A serious reward, in the millions. Such a rule would make it harder to pick henchmen, since in effect you're making them a millionaire if they turn on you.
Indeed, you have to worry that the very reason they might be joining you so easily is they plan to rat you out for the millions.
We have had a program for whistleblowers on companies that try to cheat the government, with some success, but I might suggest a good place to try a henchman law would be vote fraud. Combined with very stiff penalties (including life in prison for major vote fraud, which is effectively a coup d'etat) this should keep the conspiracies small, and less powerful.
Howoever, hacking of voting machines at the factory is a special type of vote fraud which could be done by a very few conspirators for a big result, so we still need voter verified ballots.
Of late, I've become curious about how readily we could, using certain encryption techniques, design a ballot system which would let you change or repudiate an already cast ballot, but still preserves the important principles of secret ballot. As you might guess, that's a challenge, since it seems inherent that if you can reverse a ballot you can know what it is. But it's possible some blinding algorithms might allow this.
Another option for mail-in ballots would be to provide each mail-in voter with two or more mail-in ballots. The ballots would be marked with a code, such as a red or green sticker. The voter would be told, through a secure and in-person channel, that one of the ballots is real and the others false. They must remember the colour of the true ballot. If they send in the ballot of the wrong colour, it also contains an encoded number that only the counting office is able to tell tags it as a bad ballot (and a sign of attempted voter coercion.)
The vote-coercer might have you send in all your ballots. One defence would be to have this void your vote. This allows vote coercers to use force or money to stop people from voting (which they already can do) but not to vote a particular way. Combined with my plan for secure internet voting it could allow one half of the secret ballot equation with votes cast over the internet.
Should we be able to perfect this, by finding a means for an audit trail on internet voting, this would, aside from saving much money, eliminate the problems of lines at the polls.