The Atlantic razor clam, Ensis directus, burrows underwater by expanding and contracting its valves to fluidize the surrounding soil. Its digging method uses an order of magnitude less energy than would be needed to push the clam directly into soil, which could be useful in applications such as anchoring and sensor placement. This paper presents the theoretical basis for the timescales necessary to achieve such efficient digging and gives design parameters for a device to move at these timescales. It then uses RoboClam, a robot designed to imitate the razor clam's movements, to test the design rules. It was found that the minimum contraction time is the most critical timescale for efficient digging and that efficient expansion times vary more widely. The results of this paper can be used as design rules for other robot architectures for efficient digging, optimized for the size scale and soil type of the application.