An instrument with a covered bore for subcutaneous implantation is provided. An incising body defines a non-circular coaxial bore and includes a sharpened cutting edge that extends from a bottom distal end beyond the opening of the coaxial bore and an attachment point at a top distal end. A plunger is non-fixedly contained within the coaxial bore and slides longitudinally therein. A cover is pivotally attached at the attachment point and extends down to the bottom distal end and, when closed, the cover encloses the opening proximal to the cutting edge.