Don't worry too much about it, you know how parents are. I'm sure if you had gotten the puppy your dad would have been mad. Once you brought it home your dad would have realized that "free" dog is going to cost him a lot of money. However if you think your dad was serious, maybe you could talk to him about getting another dog.

The whole situation makes me sad though, a dog is not an impulse. He should have at least charged a few dollars so that people would at least have to think for a few seconds. A dog is a huge resonsibility, especially a HUGE great dane! I worry that some of the people who took the free cute puppy are going to dump then at the shelter when they realize the puppy is going to be the size of a pony.