Although virtual inertia control (VIC) of new energy units can effectively suppress system frequency fluctuations, it struggles to actively correct frequency trajectories under extreme disturbances, exposing the system to the risks of frequency limit violations. To balance the stability of power support under general disturbances and frequency security under extreme contingencies, this paper proposes a renewable energy integrated frequency regulation control strategy for layered defense of frequency security. First, the limitations of passive response-based frequency regulation strategies, such as VIC, are analyzed, and a hierarchical defense mechanism for system frequency security is proposed. Then, a frequency security boundary generation method based on state reconstruction is proposed. Furthermore, a frequency trajectory reshaping controller with automatic activation and deactivation capability is designed. Finally, an integrated renewable energy frequency regulation control strategy is constructed by fusing VIC with trajectory reshaping control. It enables renewable energy units to seamlessly switch to trajectory reshaping control when approaching the security boundary, thereby achieving active defense for frequency security. The simulation results show that the proposed strategy does not require complex wide-area communication. Moreover, without increasing the routine operational burden of the system, it can fully tap the flexible frequency regulation potential of new energy and significantly enhances system frequency security under extreme disturbances.