In this paper, we propose to extend the Microwave Enhanced Infrared Thermography (MEIT) method for landmine detection using two excitation microwave frequencies. We present the results of a detailed modeling effort. The extended method has the potential for detecting buried objects under rough surfaces at depths greater than with the original single frequency concept. Our result shows that the two-frequency technique minimizes the clutter introduced by an irregular surface, and can lead to better detection of buried objects. A 2-D computational model of this method has been developed to simulate real-world landmine detection. Receiver Operating Characteristic (ROC) curves were generated to evaluate the performance of this new method. Finally we demonstrate improvements achieved in detection depth under rough surfaces, compared to the single-frequency MEIT technology. The theoretical results obtained so far are presently being used to plan laboratory and field experiments for validation of our assumptions.