I am building a social bookmarking service that is monetized in part by Google Adsense. However, I don't know how to influence how the ads are displayed. I think Google scans my pages and decides itself which ads to show where. Navigation on my site is mainly based on the selection of categories or tags being provided by the users. So after a user filters a list of bookmarks by the tag "SEO", I think I know pretty well what he is looking for. So I am looking for a service that allows me to show contextual ads for these particular keywords. How I can guide Google to show relevant ads? Can you recommend an alternative ad network, that gives me more control?