I think you guys are wrong. Levi is well socialized with other dogs, if a dog walks buy he will sit in the grass and watch them walk by, and cats? He loves them, he cuddles with some of the neighborhood cats all the time. He will not leave the yard. There was a big storm here last night, he was outside before it hit and a loud thunder cracked, he walked at a fast pace towards the door. Maybe I have a very smart sheltie, but my parents older sheltie Zack also will not leave the yard, again no fence.
I'm actually very surprised that a lot of people haven't trained their dogs to know boundaries. I got Levi at 8 weeks old and the training started immediately. He was house trained within 2 weeks, only EVER having one mistake in the house.
I can understand requiring a fenced yard for an adoption of a pup that is a bit older, and no longer a puppy as they may be used to that situation and it would be very difficult to break them of this.
Also FWIW, puppy's will learn from older dogs, so If you can get one trained well training another the same rule set shouldn't be too hard.