The ornamental design for a personaltether, as shown and described.
FIG. 1 is an isometric view of a personal tether showing my new design in a position of use;
FIG. 2 is a right side view of the personal tether laid out flat;
FIG. 3 is a left side view thereof;
FIG. 4 is a front side view thereof;
FIG. 5 is a rear side view thereof;
FIG. 6 is a top view thereof; and,
FIG. 7 is a bottom view thereof.
The broken lines in FIG. 1 depicting two hands represent environmental subject matter that forms no part of the claimed design. The remaining broken lines in the figures depict portions of the personal tether that form no part of the claimed design.