Deptrac is a tool recently announced by Sensionlabs. It helps you keep dependencies between the different layers in your architecture under better control by providing insight into the current state of the dependencies and warns you when unwanted dependencies get introduced.
He gives the commands to get the tool installed and how to initialize the repository with a default configuration file. He then provides an example using the Adrenaline framework and how the request/response relate to the HTTP handling. He includes the configuration changes to make for these relationships and, finally, how to run the analysis on your code to ensure the dependencies are correct.