This document describes a proposed secure scheme against power exhausting attacks in wireless sensor networks. The scheme aims to develop an energy-efficient approach to counter denial-of-sleep attacks, which can significantly shorten the lifetime of wireless sensor networks. It proposes a cross-layer design that integrates a media access control protocol in a secure manner. Analyses show the scheme can effectively counter replay and forge attacks while conserving energy. The design balances energy savings with security requirements for wireless sensor networks.