The ornamental design for a retractable dogleash with customizable casing, as shown and described.
FIG. 1 is a perspective view of a retractable dog leash with customizable casing showing my new design;
FIG. 2 is a front elevational view thereof;
FIG. 3 is a rear elevational view thereof;
FIG. 4 is a left side elevational view thereof;
FIG. 5 is a right side elevational view thereof;
FIG. 6 is a top plan view thereof;
FIG. 7 is a bottom plan view thereof; and,
FIG. 8 is another perspective view in a separated condition thereof.
The broken lines throughout the drawing figures depict portions of the retractable dog leash with customizable casing that form no part of the claimed design.