Not a fool proof system but a little helpful: In Germany you can request a second (and a third, and a fourth...) ballot. So fill out the first with fake vote,

Not a fool proof system but a little helpful: In Germany you can request a second (and a third, and a fourth...) ballot. So fill out the first with fake vote, take picture, ask for second (first one is destroyed), fill out second with desired vote. This obviously breaks down when the person coercing you is with you in the polling station.