No Access To Admin

Ok real simple question here. I'm using the membership plugin. Love it for the most part. Great for what I need. I set up 2 access levels: Pro Level and Free Level.

The free level is for regular strangers who come to the site and just wish to sign up for the social network (buddypress) section of the site and interact with others, etc. nothing more.

The pro level is for the actual client who pays our company for regular access to the admin area (posts, pages, menus, widgets, etc) of the site as well as regular site updates, etc.

Now, I've installed the admin rules and buddypress rules add-ons to accomplish this. I have everything pretty much set up, but I have a few questions. I have setup positive rules for the pro level so they can access pretty much everything, and I have a positive rule for the free level members allowing access to buddypress, etc.

My question is, in order to DENY free level members access to the wordpress admin area (since that is only for pro level) and to ONLY allow them access to the front end (buddypress) section of the site, what negative rules should I add that would deny them access to the entire admin backend area and keep them on the front end only?