4 random listings of a category in a grid

i need to show a row with 4 random listings of a specific category in a grid in the frontpage

on the frontpage editor i´m using a shortcode/html element with this

[LISTINGS orderby=rand cat=13 grid=true show=4]

it show the category, the 4 elements but NOT in random, it show the 4 latest listings

i read all the post in the forum and tried some variatons but i can´t get it to random

i know i´m close but i ran out of ideas

any help?