A good place to keep money?

I want to buy some proper art materials, since I want to go into the illustration/ design career in the future. I don’t know exactly what I will buy, as I need to do a very thorough check on everything that I might choose. I know that I should start saving now, as in 3 years or so (when I’ll be 16) I will need to buy the necessary materials. Until I will I can just practice my skills. I don’t want a savings/ bank account as I already had one in the past with over £100 on it but my parents took everything since we had some debts to pay. I can’t just keep the money around the house because every time I put the money in a piggy bank or something my parents open it . . . . I don’t want to seem like a rude brat, I love my parents and all, but I just can’t really trust them. I know I shouldn’t save and let my parents have their money to pay off the debts but I really want to save some money to buy decent art materials when I’m older. Any ideas on where I can keep the money so no one takes it?