This paper explores the effectiveness and challenges of using monitoring techniques, based on Aspect-Oriented Programming, to block adware at the library level, on mobile devices based on Android. Our method is systematic and general: it can be applied to block advertisements from existing and future advertisement networks. We also present miAdBlocker, an industrial proof-of-concept application, based on this technique, for disabling advertisements on a per-application basis. Our experimental results show a high success rate on most applications. Finally, we present the lessons learned from this experience, and we identify some challenges when applying runtime monitoring techniques to real-world case studies.