You can do what I do when I advertise on another site. Set up subdomains with 301 redirects to your main domain. Each subdomain corrolates to a different ad medium, so maybe you'll have one for Google ads, one for a banner on a site, one for a text link somewhere, you get the idea. The ad directs them to the appropriate sub which then forwards them to your main domain. Then you just keep track of the stats on thet sub domains to monitor the results.

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