Dependability is a fundamental requirement in designing sensor networks. Specifically, a sensor network should successfully detect the phenomena of interest (e.g., intruding enemy), and reliably transmit the detection results to users. To achieve the above goals, the network must have sufficient coverage, which enables prompt and accurate detection of the phenomena; the network must be fault tolerant, such that it can work effectively in face of node malfunction or failure; the network must also be secure to defend against attacks from an adversary in a hostile environment. In this talk, I will first present two distributed algorithms for efficient deployment of mobile sensor nodes to achieve a desired level of coverage. Then I will present an efficient distributed fault tolerance protocol which responds to node malfunction by relocating mobile sensors in a timely fashion to heal the network. Finally, I will briefly introduce my research on securing sensor networks.