Lhasa Apso barking like a manic...?

My Lhasa Apso freaks out when anyone is near my front door, whether it is open or closed. He barks and growls, often scaring people, despite his small size. I know it's because he is "protecting" me, but it's getting out of hand. I can't talk to anyone at the door without him spazzing out. I bought one of those devices that puts of a high pitched sound, hoping it would deter him, but now he just freaks out at that, not really helping the situation...any ideas?