The best thing to do is for sure to put it in a paper wallet, that you would hide in a safe or something like this to be sure that you will never touch it before the 10 next years. That's what I personally did with a big part of my stack.
That would help but it is more dangerous to save your paper wallet than in online wallet because your paper wallet might be loss while if you have your bitcoins online you can get the service of the good site to secure your bitcoin, the security is what matters if we are talking of a good amount of bitcoins.