Graham Keyarn wrap it in a 'for' loop
<script> var x = document.getElementsByClassName("myads");
for (i=0;i < 2;i++){
........
}
although it could overwrite the same element
so think of the setting as a maximum
If you want it so there are always the same number of ads

<script> var ads = document.getElementsByClassName("my_ads"); for (i=0;i < 3;i++){ var ad = Math.floor(Math.random() * ads.length); if (ads[ad].innerHTML==''){ ads[ad].innerHTML = 'the ad code goes here'; }else{ i--;}} </script>

If the ad has already been set it repeats the iteration by subtracting 1 from the loop count