Female GermanShepherd: problem with people coming to the house...

[gsd_love]

Hello,

I have a 5 yo German Shepherd who is really territorial, and whenever someone come to the house, the first reaction is some barking (before even knowing who it is), then if is someone that she knows well it is all happiness, BUT when it is someone who she never see before, or it's been long since she last saw him/her, she gets agressive, barking a lot, and like "going over the one who is entering" (never bite anyone, it's more like a threat), but, if the person likes dogs or is not afraid and let her smell him/her, then she calms down and "let him/her come inside"... but when someone don't like dogs, or is frighten by the "welcome" she keeps barking at him/her for long time in a threatening way.

I train her in many aspects/things, and she is in the "overall" a good behaviored dog, but this behaviour is killing me, because I can't even bring people to my house...

Is there a way I can teach her to behave or teach her that when I kiss/handshake the other person, "is because is a friend"...? Any tips or advice?

Thanks a lot.

(sorry for my non native English)