My name is Jack!

We found Jack on the road two years ago. He had been dumped on an Amish farm, and they didn't want him. He's a sweet boy, great with my little kids, other dogs, and cats. However, he is a master escape artist and I've been unable to keep him contained in our fenced in yard. We live on a dairy farm and have delivery drivers/milk haulers/etc coming all the time, and Jack has become possessive of his territory. He shows aggression to anyone outside of the family and he has become a liability.
Also, the school bus made the mistake of allowing him to ride the bus, so now he runs down the road and the bus stops and picks him up and then drops him off with the kids. Very cute and the kids find it amusing, but a bad habit.
In the house, Jack loves to snuggle and is a wonderful pet. He knows the sit command and is crate trained.
I think he would do well being leashed while taken outside, rather than having the run of the yard like he does at our house, and being unsupervised.