The ornamental design for a privacyfencesupport, as shown and described.
FIG. 1 is a front perspective view of a privacy fence support showing my new design;
FIG. 2 is a left side view thereof;
FIG. 3 is a right side view thereof;
FIG. 4 is a front view thereof;
FIG. 5 is a back view thereof;
FIG. 6 is a top view thereof;
FIG. 7 is a bottom view thereof; and,
FIG. 8 is an environmental, perspective view with the broken lines showing a partial fence, and a bracket being for the purposes of illustrating environment and forming no part of the claimed design.