In this article, we develop a unified analytical framework for investigation of the ergodic secrecy rates of cooperative decode-and-forward relay networks in a myriad of fading environments. We utilized an exponential-type integral representation for the logarithmic function to derive an approximate expression for the ergodic secrecy rates of cooperative decode-and-forward relay networks only in terms of the moment generating function (MGF) of signal-to-noise ratio (SNR). We show that cooperative relays can be exploited to enhance the wireless physical layer security of the classical Wyner wire-tap channel. Numerical results are presented to investigate the impact of channel fading statistics, location of the relays, number of eavesdroppers as well as power allocation on the achievable ergodic secrecy rate.