The explosive growth of wireless communications lately imposes novel challenges for radio spectrum usage and policing. Many new communication scenarios have emerged that necessitate techniques for precise spectrum availability estimation and subsequent optimal spectrum sharing. For this purpose, estimating and validating the spectrum availability and policing its appropriate usage represent very important aspects of wireless network planning and optimization. This article discusses various approaches for spectrum availability evaluation, calculation and correct usage combining several case studies developed in different countries. In particular, it offers insights into simulation, modeling and measurement-based methodologies related to spectrum utilization and appropriate usage focusing on the effects before and after the digital switchover (DSO) of the television system. We investigate the usability of the different propagation models for wireless systems modeling, including the measurement-based validation of their precision for different scenarios. The article, furthermore, presents laboratory experiments targeting various aspects of DVB-T and LTE-800 coexistence, as a cheaper alternative to the measurement campaigns for fast and satisfactorily accurate results in controlled laboratory environments. Finally, the article discusses an example of a nationwide monitoring system for intruder detection, comparing several applied methods and their precision, which is important for constant monitoring of the spectrum usage policies, set by the spectrum regulatory institutions.