You're creating a SharePoint portal that contains a mix of content, including dashboards. Some of this content is intended for all users; some is highly sensitive and meant for only a few clients. You need to neatly manage the separation of public and private content.
First, you'll need to use user roles and group memberships to secure the sensitive content. When you've done so, the content that users will be able to access on the portal will change dynamically, based on their permissions.
The next step is to organize the site so that access (or the lack thereof) is transparent to users. An effective way to arrange the content is to group elements horizontally. Place the standard content that is targeted to all users at the top of the site; place the highly sensitive content that is available for only a few users at the bottom of the page, as Figure 1 illustrates.
Then use SharePoint's audience-targeting capabilities to show or hide the sensitive content area, based on users' membership in a particular audience group. (Remember, you can use audiences to show or hide content, but you must use access control to secure content.
For more information on this strategy, see "Hiding and Restricting Information: Audiences and SharePoint Security."