Good points, though they're rather at odds. If you assume voters will mess up their ballots that frequently then the voter being coerced can just find a ballot

Good points, though they're rather at odds. If you assume voters will mess up their ballots that frequently then the voter being coerced can just find a ballot that's close to what they were coerced to do and say they messed up the rest. No way to prevent surreptitiously taking more than one strip of paper comes to mind. Someone should be observing the voters take the strips of paper to ensure only one is taken, but that doesn't prevent sleight of hand. But if there are mail-in ballots, you've already basically given up on voter coercion anyway.