You can say 'stop' or 'alto' or use any other word you think will work but I've found that a large bore muzzle pointed at someone's head is pretty much the universal language.
Clint SmithThe sling is to a rifle what the holster is to a pistol. If you have a sling, chances are you will keep the rifle with you. If there is no sling present, you will set the rifle down. When you are at the absolutely farthest point away from the rifle that you can possibly get, you'll need it.
Clint Smith