I Like what your doing
But if I May make a suggestion, I would make it 2 trys, If they can't get it from, what your site is suggetsing, they never will, I found this on a lot of the sites I was Involved in.

Another Idea is members sign in, then you know who is members and who isn't, We did that so when the guest's try and place their posts, they had 2 posts unless they became members (this worked pretty well, unless, they were given the answer straight away), then it fell down

I must admit we are still working on this (though LOTR is pretty close), our group has taken that into consideration, If you solve it LOTR, I would be really interested on how you did it

Sgt