How to keep child from deleting DS save profile for Mario?

I just bought one of the Mario games for my 3 year old. I believe it was super Mario brothers but not positive. Anyway my husband started playing it the other night while my son was sleeping and he got to about world 6 then my son deleted it the next day and hubby got really upset. He spent a couple hours getting back to where he was last night and he wants me to keep my son from playing it just until he beats it. But it's my sons new game and he wants it. Is there anyway I can keep my son from deleting his file. Like maybe a way to back it up some how? Because he knows exactly how to erase and he seems obsessed with doing it lol.