Protecting site against negative SEO

Hi, I have a website that offers two different versions of the same service. Currently, I have 2 pages about the same topic. One is for a limited free trial of the service and the other is a sales page. I`m concerned Penguin is going to nail my website for duplicate pages with the same topic. I think the obvious answer is to use rel canonical on one of the pages but I can`t since I`m already using that tag on both pages to help protect against negative SEO. I don`t want to combine the 2 pages into 1 since the content would be too long and not appropriate. Your thoughts on this would be appreciated. Would the rel=next & rel=prev be of any use here? Thanks in advance!