My dad is considering getting a tattoo of the date we lost our baby, and I don't want him to.
That's hard. Why are you against the tattoo?
I don't want to think of our baby dying.
It's understandable that you'd want someone to respect bad situations more. You should make him see the error of his ways.
He's my dad. He should already know. I shouldn't have to fight with him about it.
He is your dad, but he's not a mind reader. You need to communicate how you feel to him before he does something permanent that he can't undo.