Cesar Millan recommends using a consistent non-mark (the tsch sound) when a dog is misbehaving. If the dog continues to misbehave, it is important to follow-up the non-mark with some action (e.g. a body block or time-out) so that the dog understands that there are consequences for ignoring a non-mark.
In the 16 years that I've worked with fearful dogs NEVER have I read a book more informative, applicable, and truly positive results oriented as this one. Finally, a book about fearful dogs that actually cares about the nature and root of the fears the dog is experiencing.
Brain Games for Dogs: Training, Tricks and Activities for your Dog's Physical and Mental wellness (Dog health,Dog tricks, train your dog,interactive games ... How to train a dog Book 1) - http://www.thepuppy.org/brain-games-for-dogs-training-tricks-and-activities-for-your-dogs-physical-and-mental-wellness-dog-healthdog-tricks-train-your-doginteractive-games-how-to-train-a-dog-book-1/