How to persuade your parents to get you a dog ?

I am a 15 year old boy from Ireland . I have had 2 dogs so far and both didn't really go to well. 1 was a rescue dog which was eggressive and the other was a beagle which needed more space then we could give it . i want to get a boxer dog within the next 2 months but dont know how to persuade my mam and dad into buying 1 for me > any advice ?