In most cases, participants must declare their support for a candidate in public, but not always. That's the way it has been done, although secret ballots could be the method of choice if decided when the caucus rules are set for each state.

In Texas there's a law that requires employers to allow/encourage their employees to participate in caucuses. The claim that working people couldn't leave work to vote is bogus. Also, the lines at voting precincts are long, so long lines for caucuses is also a bogus excuse.

The main reason Obama did better than Clinton is that his campaign was more organized and enthusiastic with a positive attitude, and he doesn't have to depend on crossover mischief to get votes. His crossover votes are mostly from people who are switching parties for good.