I want to babysit, but my dad won't let me?

I'm very responsible and I have initiative, I'm also great with kids, I'm always the one at family reunions watching over my little cousins. (who are between the ages of 3-9) My family is poor and my dad is out of work so my parents can't give me spending money, so I really want to earn some of my own, particually by babysitting. I don't have a license, but I know basic first aid and childcare. I don't really know many of the people at my apartments, but there are a lot of kids and I've asked my parents if I could be a babysitter, my mom is fine with it, she says it'd be a great summer job and a good way to learn how hard it is to earn some cash. I'm even willing to let my parents use my earnings for food and gas, since we can't afford many neccessaties and I'd like to help. But my dad says no. I've asked him twice but he just says no and I don't want to ask him again, especially since my mom told me that he told her he was getting angry about the idea. He did explain to me his reasons for saying no, which are that since I'm a minor, if something happens to the child he and my mom will be the ones arrested, and our neighborhood is kinda dangerous. I agree with these reasons and respect them, I never argue with my dad but this is something I want to do very badly I don't want to be a pest about it, I have been trying to show him that I'm mature for my age and that I'm up to it. Any suggestions on how I should confront him and persuade him to let me babysit, or at least have a "trial period" so he can see if I'd be good at it? He's a great dad but he hates trying to be persuaded and like I said I don't want to be a pest. What do I have to do so that he'll alow me to take up babysitting as a summer job?