Maybe you could set up a page for the monthly Bryce challenge that states all the rules, and when somebody wins, that page would be where they would post the topic for the next challenge. That way in order to find out the topic, people would have to at least see the rules. (Whether they would actually read them is, of course, another matter.) That page could also be where you post the list of pics for voting and announce the winner, with a permanent link to it at the top of the Bryce forum like the FAQ. Just a thought.