The ornamental design for a retractable dog leash, as shown and described.
FIG. 1 is a perspective drawing showing top, rear and left side views of my new design for a retractable dog leash.
FIG. 2 is a perspective drawing showing top, front and left side views of my new design for a retractable dog leash.
FIG. 3 is a perspective drawing showing bottom, rear and right side views of my new design for a retractable dog leash; and,
FIG. 4 is a perspective drawing showing bottom, front and right side views of my new design for a retractable dog leash, with the bone-shaped handgrip removed for clarity of disclosure.