The meaning of the dream symbol: Dog

A dog may symbolize your 'animal' nature, particularly if you haven't yet accepted that you have an animal nature!
It the dog is frothing with rage, this might indicate some repressed part of you is now ‘at the end of its tether' and will cause a lot of trouble if not given attention and allowed its proper place in your life.
If the dog is paired with, say, a wolf, then it is the wolf that will symbolize your animal nature, and the dog (if its emotional ‘feel’ is contrasted in the dream with that of the wolf) will represent some ‘higher’ part of your nature.

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The dog may stand for some person you know, in which case the dream will be telling you something about the person’s character or expressing what you feel about the person (that he or she is a ‘dog’ or a 'bitch').

In a dream, a Dog may represent a number of complex emotions, including fear, friendship, loyalty and obedience. A dreamer needs to completely determine the color, demeanor and intentions of the dog and compare these characteristics with the landscape encircling the animal. For example, if a big, yellow dog seems friendly and leads us away from a particular location or situation, we may need to analyze the ‘hidden shadows’ and/or deceptions involved in the place or circumstance itself. In this example, a dog may reveal our own apprehensions, which we have foolishly, chosen to ignore. On the other hand, if the dog is fierce, foams at the mouth and chases us through our own home, we may be experiencing distrust in an individual very close to us. In yet another symbolic association, that being the Chinese zodiac; the dog represents honesty and generosity, in this representative case, a dog is a straight forward companion with no ulterior motives except unification and bonding trust.