How to get dad to let you have a puppy!?

I have tried to convince him for over a year. What has worked for you? Have any suggestions for what to do? I thought about just going and getting one on my own becuase I know he wouldn't just get rid of it. But then theres my stepmom, she is the one who doesn't want me to have one. She has my dad wrapped around her finger. She just makes my dad tell me no so she doesn't look like the bad guy. She said I could once not thinking my dad would actually say yes and then I couldn't get one again. Help meeee.