An attack to the base station (sink) in wireless sensor networks (WSNs) may make the entire network to be invalid, Therefore, it is very necessary to conceal the physical location of the sink in certain circumstances. In view of previous studies has all assumed a weak adversary model. Through a Linear Programming (LP) framework we present two different sink hiding methods: fake sinks (FS) method and balanced flows (BF) method. By simulation we analyzed and compared two methods with respect to their impact on network lifetime. Our results show: (1) The impact of preserving sink unobservability on network lifetime is considerable; (2) Network lifetime with BF is better than with FS in large networks.