What to do about my parents' neglected dog?

I posted yesterday about taking my parents’ neglected dog, a Great Pyrenees mixed with I believe Golden Retriever. He is 4 and has lived outside his whole life. He has a large backyard with a dog house that has straw in it. They live in the country. He is overweight and fed lots of table scraps or leftovers from restaurants. He is seldom paid attention to and cries every time I come over to visit. He hasn’t been to the vet in who knows how long and his fur is matted. He desperately wants attention. I decided to welcome him into our home and I called my parents to let them know. I explained my concern that I didn’t want them to get another dog and have it be placed in the same situation. My dad laughed at me and said that was none of my concern. They think the dog is fine outside and it is his job to protect them. They decided not to let me have the dog b/c my mom wants a dog in the yard, but if he gets out of the yard again they would bring him over. He gets out of the yard sometimes.