How to persuade my parents to get a rescue dog?

So recently, ive really been overtaken by the thought of adopting a dog from my local SPCA. My family all has said before if we were ever to get another dog, it would be a big one, as we already have a medium sized dog. However, when i talked to my mom about it, she simply said that she was for it (i dont know if she actually is or if she;s just saying that to make me happy) but my father would never go for it. When i got her to talk to my dad about it a bit more, he said that his main resoning was that we couldnt have it around the bunny. See, i have a bunny who runs around my house free, using a litterbox and just going wherever he pleases. When we first got our bunny, we had to go through about a threee week process of introducing her to my dog, and getting them comfortable around eachother. Now they're best friends, and snuggle all the time. My parents think this would be too hard to do with a new dog we hardly know, but i think that anything is possible, and over time, with hard work, we can get them to be friends like my other dog. My parents just wont listen though! Were a family of five, with three kids all over 16, so were all mature and love taking care of animals, so i know this is something we can handle. How do i convince my parents to save this innocent animal?!