1. A tissue stimulating prosthesis implantable in a recipient to electrically stimulate a segment of the recipient's tissue with stimulating current, the prosthesis comprising: a stimulator unit configured to generate the current signals; a first electrode configured to direct stimulation to the tissue; a second electrode positioned separate from the first electrode; and a variable impedance shunt disposed between the first electrode and second electrode; wherein the stimulator unit is further configured to selectively control the shunt impedance.