Voter fraud has be going on in the United States since we've been voting. Kennedy pulled a great turnout from the cemeteries in Illinois to win in '60, the Philly area's reknowned for it in PA, Wisconsin's suffered from multiple bumvotes the last several cycles, there's some blackbox questions in Ohio.... it happens.
The only way to ensure a "fair" election would be to break it into smaller "neighborhood" components. Each team of captains would be responsible for around 50 eligible voters in his area. The team would then report to a quarter precinct then up to a half precinct and they'd report to the precinct level (similar to what we have now) and so on up the food chain.
The problem with this is that it would take days to get the final tallies and our society is all about instant gratification so it wouldn't fly. If Bush/Gore taught us anything though, it should be that the republic survived without knowing the results election night.