I spend a couple of days away from the internet and things happen!
Google now allow you to split a page into sections with the idea that Adsense ads are only targetted to the text in that section. A couple of comments is all you need:
<! -- google_ad_section_start -->
<! -- google_ad_section_end -->
Apparently Google only take this as a suggestion but in some situations it could help. Of course sticking to one topic per page is better nearly all the time anyway.