Physical-layer security has become widely recognized as a promising technique to enhance wireless security by exploiting the characteristics including fading, noise, and interference. This letter explores an opportunity to enhance physical-layer security by balancing the power expense between pilot and payload signals without any prior knowledge related to eavesdroppers. In lieu of presuming perfect channel acquisition, we consider a practical wiretap channel with the receivers enabled by pilot-aided channel estimation (CE). The problem is tackled by accounting for the network interference from cochannel interferers in unknown locations by which the secrecy level is significantly affected. Specifically, the secrecy transmission rate (STR) reflecting the CE errors is derived for the worst-case within the use of a protected zone. We investigate the feasible region of pilot and data power allocation under reliability and secrecy constraints, and the optimal power allocation for pilot and data to maximize the STR is proposed, whose performance is verified via simulations.