Using Access Levels in Membership

I am setting up my access levels for a new site, and I have an issue. This is for a visitor who is not logged in. I have a home page that has a list of posts, with a thumb, and an excerpt to the full post. I want a visitor to be able to see the home page, just to see an example of some posts, but when they click through to the actual post, I don't want them to see it. I tried restricting them by using a negative access level for categories, but the posts on the home page disappear because they are also part of the category. Any thoughts on how to accomplish what I am trying to do?

Thanks!