Lack Of New Members

I have tried every trick in the book in order to get new members to join our forum but I'm left continually frustrated as either no ones signs up or those who do either don't post or spam for their own site. Is there some kind of secret I'm misiing. I know it helps to have an active forum in the first place and I think ours isn't too bad but the only way to make it more active is to get more sign ups... I'll keep on trying and post my findings. Until then if anyone is interested in signing up go to http://www.websitetoolbox.com/mb/frazzle_f