If you have more than one banner on a website page, it’s easy to ensure that you never show the same banner twice with the OpenX ad server.
Provided you are using Single Page Call, or the Javascript zone tag, the Local Mode zone tag or the XML-RPC zone tag, then under Tag Settings on the Invocation Code tab, you can set the “Don’t show the banner again on the same page” option, and OpenX will ensure that the same banner is not shown more than once on a page.

The "Don't show the banner again on the same page" option.
There is also the “Don’t show a banner from the same campaign again on the same page” option for Single Page Call and these three zone tags, which can be used to ensure that every banner on a page will be from a different campaign.
Of course, you can use both options if you want to ensure that not only is every banner on a page from a different campaign, but also that there are no duplicate banners.
