What you could do is create ten different pages. Each page with the banners in their new positions.

Then, have the link that goes to those pages, be a random link.

Each time someone follows the link to the Agents Pages, they end up at a different page.

And to stop people from bookmarking one of the Agents Pages, you could have a small Javascript at the top which reads where they came from. If they didn't come from the main page they're automaically diverted back to it.

Hope this helps.

Michael Ross.