The advent of frequency-agile radios holds potential for improving the utilization of spectrum by allowing wireless systems to dynamically adapt their spectral footprint based on the local conditions.  Although a number of approaches ranging from market mechanisms to opportunistic usage have been proposed, a clear picture is emerging, that spectral gains can only be realized through real-time adaptation at runtime. However, this leaves open the major problem of how to enforce/incentivize compliance and what the structure of “light-handed” regulation should be. This work examines this in the cognitive radio context and focuses on two specific technical problems: (a) determining whether harmful interference is occurring and (b) assigning liability by detecting the culprits.