Help persuading my parents to allow me to have my own dog?

I know i had to talk my dad into letting me keep my dog but he is big and he was stray and what i did was showed him how much i care for it and play with it and prove to him that you should be able to have a dog and you need to prove to him that it will be your responsibility and you will feed him give him water play with him and bathe him PS. If this doent work you could always pull the fake tears trick :).