The ornamental design for a rodholder, as shown and described.
FIG. 1 is a front perspective view of a rod holder showing my new design;
FIG. 2 is a front view of the same;
FIG. 3 is a back view of the same;
FIG. 4 is a right side view of the same;
FIG. 5 is a left side view of the same;
FIG. 6 is a top view of the same;
FIG. 7 is a bottom view of the same;
FIG. 8 is a back perspective view of the same; and,
FIG. 9 is another back perspective view of the same.
The broken lines of the various views, namely the oval head thumb screws of FIGS. 1-9, the shovel and fishing rod of FIG. 8 and the fishing rod of FIG. 9 are included for the purpose of illustrating environmental structure that forms no part of the claimed design.