We had just trained our collie on the invisible fence when we got Max. They both learned quickly but she just hugs the house whereas he learned the boundaries well and uses the whole yard. It is working really well. He seemed to pick up on the flags right away and now listens for the beep if he's trying to get a ball near the border. He penetrated it only one time when trying to follow me on a walk. I think that is the only correction he ever got. I tested it on my hand and it is more startling than anything, not painful. I like it especially because I don't have to worry if the dogs follow kids out the front door.
It's not so hard to teach them that they can leave the yard in the car or on the leash.