Drupal Community Portal

Hi, I am applying marketing tools to Drupal development and one of those is tracking the source of a link dynamically. For instance, in some sites I've seen this as www.example.com/foo?src=google. I don't really know how flexible this is, but I want to be able to have metrics about the sources and to use these variables to dynamically adapt the content to the source and to be able to create custom URL if they help discriminate their source. Uses of this is such as presenting a promotion for a prospect who comes from Twitter.
Is there a module that enables this? What's the best practice?
Thank you.