How do I get my mom to buy me a dog?

Well I can't convince her to do it but i would like to have a dog i am an only child living with 1 mom and 1 dad with g fish and 2 turtles i asked her before and my dad took me to the pet store and bought me a fish then i asked again my aunt gave me 2 baby red eared sliders i have been training my turtles too eat from my hand it works ok and i train them to do tricks but hey it's a turtle! and lol they can run in a hamster ball