I love when people come into my office and tell me, "This is my Alpha-Female dog so you better watch it". Or, "This dog is an Alpha-Male. If I don't put him on his back every so often he'll think he's in charge." Bad trainers, especially with TV shows, and ignorant lazy people on the internet only make things worse. Punishing your dog, especially after the fact usually only makes things worse.
Consider these statements culled from the American Veterinary Behavior Society website (www.avsabonline.org) as summarized in the January 2008 Compendium for Small Animal Practice:
It is difficult to correctly time punishment.
Punishment can make the undesirable behavior worse.
To be effective punishment must be sufficiently intense, but when administered at high intensity, it can lead to physical harm (to both the pet and the owner).
Any punishment may make the dog fearful, which may lead to fear behavior at other times.
Punishment may intensify or even initiate aggressive behavior.
Punishment may cause unwanted behavior changes, some of which may mask early signs of aggression.
Punishment may associate the wrong trigger (such as the owner, an environment or other animals)with the unpleasant experience.
Punishment often does not address the actual problem, or show the animal the correct behavior. (Rubbing the dog's nose in poop just makes him run when you come home. It does nothing about the fact that you were to lazy to house train him properly.)
The AVBSA website is a great source of information. As with any program though, you should talk to your veterinarian before you start a program. You would be surprised at how many dogs that just started peeing in the house had urinary tract infections, or how many new biters had arthritis.