Have you played yet? If so, were there lockers to rent at your local field? That could be one way to compromise. Have you taken your Dad to play? Do you have the money for the marker, or are you expecting your parents to shell out dinero on what they see as a way to hurt you? Your parents know you best and if they are reluctant to let you have a marker, what have you done that would lead to that? A promise from a person with no credibility is just a whiff of hot air. Take steps to build your credibility and show that you are responsible, such as doing chores before you are nagged and starting a small business to earn your own money; like lawn-care, paper route, etc. Do not buy one without their approval and then hide it at your friends and sneak around behind their backs. You definitely won't earn any credibility or trust that way because they will find out. They always find out. That's why they're the parents. Good luck. If nothing else you can always use the rentals.