[kh99]

I think you might be able to disallow any bbcode between url tags by creating a plugin using hook bbcode_fetch_tags and code like this:

if (is_array($tag_list['option']['url']))
{
    $tag_list['option']['url'][''stop_parse'] = true;
}
if (is_array($tag_list['no_option']['url']))
{
    $tag_list['no_option']['url'][''stop_parse'] = true;
}

ETA: Unfortunately it just occured to me that this would make it impossible to make a clickable image.