Teeny, I'm sorry about your dog. :(
Your dad sounds a lot like my dad. My dad hates the vet too and we kept our old boxer until it was so painfully obvious that we couldn't anymore.
She was 9 (boxers usually live 8-10 years). She had some sort of awful neurological condition I think. One day she started backing into a corner uncontrollably, couldn't stop doing it. The most terrifying part was when part of her skull caved in, a sign of serious neurological problems. It was clear she couldn't fight anymore after that, even my dad realized. ;-;
She was also covered in little tumors (well one was kind of big) but the vet tested one of them and said it was benign. Apparently boxers get them a lot.
I wish I had photos of her but they aren't on my computer. She was a dark brindle boxer with a little white stripe between her eyes. My first dog. She bit my face the first day we had her.