what i mean is have some questions that need to be answered at the registration. questions that require real, typed answers. why do you want to join? what neighborhoods in irvine are your favorite? it can be anything but the simple fact that something has to be typed out can be a deterrent, but the actual content is irrelevant.
same goes for email verification. if you have to set up another email acct, answer some questions, register, wait for verification, just for the purposes of trolling a forum, maybe its not worth the time.