Counter Unmanned Aerial Systems (C-UAS) is an emerging area of active research and development especially since the Ukraine war. A parallel stream of research and development is also taking place addressing the defensive survivability of friendly unmanned platforms against hostile C-UAS threats. While extensive literature addresses offensive C-UAS capabilities, the complementary challenge of defending autonomous platforms remains profoundly underdeveloped. We call this research and innovation direction Counter-Counter Unmanned Aerial Systems (C2-UAS). In this paper we present aspects and directions in radio C2-UAS domains. For R F systems, we address radar crosssection reduction through phase centre manipulation, geometric shaping and advanced materials. We also discuss communications link resilience against jamming through anti-jamming techniques and low probability of intercept/detection (LPI/LPD) waveform design, and navigation resilience through Global Positioning Systems (GPS) anti-spoofing mechanisms and multi-constellation Global Navigation Satellite System (GNSS) redundancy. We identify critical research gaps, emerging technologies, and future research directions especially by a brain-inspired architecture to foster C2-UAS. This work establishes the theoretical and practical foundations for C2-UAS as a distinct research discipline with profound strategic importance.