Prominent requirements such as high data rate demands across weaker coverage areas have lead to the utilization of cooperative communication system in fifth generation (5G) networks. In this regard, this paper presents a novel joint transmit power sharing and relay placement scheme for decode-and-forward relay assisted secure communication to a legitimate user in the presence of an untrusted user. Observing that the joint secure rate maximization problem for the trusted user is non-convex, first we present key insights on optimal power sharing between source and relay, and then derive an equivalent single variable problem on relay placement. Next, tight analytical bounds for optimal relay placement are discoursed to ultimately come up with a computationally efficient joint global optimization algorithm. Lastly, the selected numerical results validate the analysis and highlight the substantial gains achieved by the proposed joint design over benchmark scheme.