I have read the following books and I would recommend them to help you understand dogs, Australian Shepherds and herding!

Das Kosmos Erziehungsprogramm für Hunde
Nicole Hoefs Petra Führmann

Erziehungsspiele für Hunde
Nicole Hoefs Petra Führmann

Handbuch der Hundezucht
Inge Hansen Verlag Müller Rüschllikon

Hundezucht
Dr. Helga Eichelberg Kosmos

Australian Shepherd
Liz Palika

All about Aussies
Jeanne Joy Hartnagle-Taylor

The owner's Guide to Australian Shepherds
Joseph Hartnagle T.F.H Publications

Hirten- und Hütehunde
Karl Hermann Finger

Ausbildung von Hütehunde
Hans Chifflard Herbert Sehner

The Farmer's dog
John Holmes The anchor Press Ltd.

Herding Dogs progressive training
Vergil S. Holland Howell Book House

Sheepdog Training an all-breed approach
Mari Taggert Alpine Publications

Training and working dogs for quiet confident control of stock
Scott Lithgow UQP Paperbacks

A way of Life
H. Glyn Jones Farming Press Books

For second-hand books try www.abebooks.com