If you take note of the exact wording and advertisement, or better yet, mouseover the ad and it should tell you the url which you can then copy, or you can also get a screenshot of the ad, then use the 'Contact' link at the bottom of every page to let Dave know. That way he can hunt down the offending ad.
We also have a Site Forum (check under Forums tab) where you can ask about things pertaining to the site. If you start a brand new thread over there, Dave is sure to see it.
