In all honesty, I like the implementation Estonia is doing.

In effect, your identity card allows you to vote as many times as you wish. You cannot see your vote, but the newest vote overwrites the previous vote.

This means, that if you are coerced to vote a certain way, you can simply make another vote and wipe out the previous one.

The only downside is this would require a national ID program, which many religious extremists are very much against.