I have been on my dog like white on rice since we got her at 12 weeks. She is always in training and that keeps her within the bounds of reason - if she were not properly trained she would be unbearable.
I have a lab border collie cross and we had gotten him from someone who kept him in a cage all day and was going to put him down simply because she didn't have the time for him. When he came home he had all sorts of agression and herding issues, especially with small children and the cat, but now he's as sweet as can be. We didn't let him get away with a darn thing, and it worked.