A method of stimulating a portion of a spinal cord of a patient includes identifying an arrangement of electrodes including a relative placement of each electrode within the arrangement; identifying a vertebral level for implantation of the arrangement and a position of the arrangement with respect to the spinal cord; determining by calculation, for a selection of at least one cathode from the electrodes, at least two anode guard electrodes from the electrodes including in the calculation an estimated thickness of cerebrospinal fluid at the vertebral level; and stimulating the portion of the spinal cord of the patient at the vertebral level using the at least one cathode and the at least two anode guard electrodes.