The ornamental design for a guardsupportingmember for a gabion basket, as shown and described.
FIG. 1 is an isometric view of my new design, a guard supporting member with two (2) prior art gabion baskets shown in broken lines to illustrate the environment of the claimed design and forms no part thereof.
FIG. 2 is an isometric front left top view of the guard supporting member shown in FIG. 1.
FIG. 3 is an isometric front right top view of the guard supporting member shown in FIG. 1.