You do NOT need anything, just electrical tape. Do NOT use masking tape or any other type....use electrical tape.
I have seen trackers ripped of shock cords, even with duct tape, cannot emphasize this enough.
Just tape tracker to shock cord, completely wrap tape around the entire tracker, that will be plenty good to protect it.
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Do NOT tape the antenna to shock cord [unless the owner insists].
Been doing this for many years and haver never burned or blown up a tracker, even with rockets using 7gram charges.
Good luck.