We investigate a covert channel implemented on top of MAC protocols that are based on splitting algorithms. Covert information is embedded in nodes' splitting decisions. The covert channel can operate in three modes. The conservative mode is the safest in the sense that use of the covert channel is undetectable. The aggressive mode generates best throughput, but is more vulnerable to detection. A strategic mode is also available which allows the covert users to make a tradeoff between detectability and covert capacity. Simulation shows that the covert throughput ranges from 0 to as high as 0.3 bits per slot, depending on various parameters. It is easy to implement and very difficult to detect.