I claim the ornamental design for a snap-on connection retainer for extension cords, as shown and described.
FIG. 1 is a perspective view of a snap-on connection retainer for extension cords showing my new design; the broken lines show environmental structure for illustrative purposes only and form no part of the claimed design;
FIG. 2 is a side elevational view thereof, the elevational view of the opposite side being identical thereto;
FIG. 3 is an end elevational view thereof, the elevational view of the opposite end being identical thereto;