I'd be surprised if much of the dirty tricks happen while the voting is taking place. The time to stuff the ballot box with illegal votes will either happen *before* the polls are open or *after* the polls are closed, when there is nobody around except the election folks to tamper with the ballot box.
If Democrats run the elections in your precinct, show up early with a camera and stay late. Ask to follow the box all the way to the courthouse.
If they resist, say "If your work is honest, you have nothing to hide from me." Tell them you are one of the DNC's "10,000 lawyers"...that'll maybe let their guard down.
Don't campaign or politic or even make comments about anyone in political office. Come across as being apolitical as hell but watchful as a fox.
Evil does their business best in the dark.
Oh, and don't forget you can still use a camera even after the film has run out... :-)