I have two dogs, one of which was abandoned close to where I live. A properly qualified canine behaviourist diagnosed him as suffering from fear aggression as a result of the treatment he had received prior to being abandoned. He was frightened of people, other dogs, cars, the vacuum cleaner etc. and reacted agressively when confronted with these and other situations. The long,slow process of building up his confidence requires various methods of reducing his stress levels and I have found that Turid Rugaas' book has been an important tool. I am still amazed that when confronted, for example, by an approaching car his stress level visibly reduces when I yawn.