Aquagility - I agree it's a difficult one to solve and I agree "policing" is not possible (my username is not connected to policing, it's football related and reasonably easy to work out if you include the number).
However, I disagree that the onus is with the quiz setters. Yes, they could ask entrants to sign an undertaking, but surely the problem is with the quiz entrants (some of them anyway). They are so desperate to get the answers, they'll go to almost any lengths - ie. posting so many questions on here and, more often than not, soon after the quiz has been published. I may have old fashioned principles, but I was always taught about hard work and pride. If I can't find an answer myself, I'll happily have a guess or leave a blank space - I just can't see the point of cheating.
What amazes me is that most of the charity quizzes are for very small sums of prize money, yet people are so desperate to submit a complete entry, they go to any lengths. The important thing is to help the charity (and people don't need to cheat to do that). I can understand it a bit more with GBQ and GFQ, but it's still wrong - and it's the posting of questions/answers that is killing GBQ and the like.
People have asked on here for the name of the quiz to be stated (that is often ignored), not to ask too early (again ignored). Possibly, an answer is to make them feel guilty about asking, but how? I also doubt these people have any ethics, so it would be a pointless task.