I had to deal with this from my dad when my daughter was born. At that time, the only dog I had was a Great Dane...he wasn't too fond of the Dane, but you would have thought the world was coming to an end when I decided to adopt Mindy Lou from the pound!
He outright told me I was a bad parent for keeping my daughter in the same house as a potential killer.
Watch out! She may smother you with her tongue or whip you to death with her tail!
As you, I've tried explaining the myths and debunking them, I've tried face-to-face raw PROOF...I've sent pictures, I've done about everything I can think of, but still nothing. He hasn't said anything lately, but he does let me know whenever there is another headline on the news about a "pit bull" mauling...quotations there because in this area it may say "pit bull" but in reality it's usually a mix or a completely different breed. Maybe he's started to shut up about it because he's seen that nothing is going to happen...it's been nearly four YEARS, and I now have four pit bulls in my home and besides some DA with only one of my dogs, I have a harmonious home.
My dad frustrates the hell outta me though, bless his puny head. He approached my husband and my religion with the same crap (prejudiced). My husband is from Puerto Rico, and my dad has always been against interracial dating/marriages...then he got to know him and it's a different story. And from the same man that swears a pit bull's jaws lock, came "the only thing I've heard about your religion is that you dance naked in the woods and have big orgies."
I'm Wiccan BTW. You'd think after being proven wrong so many times he'd finally see the light, but no such luck. Sometimes you just have to let it go in one ear and out the other and realize you're an adult and can make decisions on your own (i.e. marriage & kids).
LOL my rant is over...and in case he ever reads this...I love you Daddy despite your flaws!