My dogs are 4lbs 9 oz and 6lb 9oz and I have had an invisible fence a year and a half and I love it! I go out with my dogs, they have the freedom to run the length of my yard (which is a good length) They love to go out and chase each other with out getting tangled in a leash. My dogs love to chase squirrels, birds, also one loves to follow cars but they have never chased them past my yard. People walk there dogs past my yard and runners run by but my dogs never leave the yard unless on a leash. They do need to be trained to stay in the yard the correct way before the shock function is even turned on and they really haven't been "shocked" very many times I could count on my one hand how many times, I put the device on myself and it really isn't bad, they have a device to put on the collar to minimize the "shock" to 50% and that is what my dogs have, I actually had to take it away from my 6 yr old nephews because they were shocking themselves with it for fun (kids!
. There were issues when I first bought the system, we have a town carnival each year and people park at the border of my yard, a few cars were parked over my fence and one of my dogs did get out and my neighbor caught her for me since she ran to him (it was also soon after it was installed and they were still in training) so I will have to put up either signs or caution tape this year (I probably with put them on leashes also for the carnival), but other than that they have never ran off. I would be worried of other dogs that came into my yard or even coyotes so I do go out with them. But even a regular fence wouldn't protect against hawks.