I have four dogs--different breeds, different personalities, different temperaments.  All have come from homes where the original "owners" tired of them for one reason or another.  This motley crew did not immediately become a happy pack.  I had no idea how to deal with the problem.  Then I watched Cesar Millan's Dog Whisperer--over and over.  I immediately began to use Cesar's approach: seeing myself as the pack leader, exercising the dogs more (and together!), behaving more like the dogs' mothers would have behaved (yes, I applied a bit of pressure to the neck with my fingertips--the Mom "bite").  Now I have a happy, peaceful pack of contented, well-exercised, balanced dogs.  And I am a happy, peaceful pack leader.  Now my dogs are not a source of frustration and guilt, but a source of joy, love, and connectedness.  Cesar is a wonder!