I got this one: www.amazon.com/dp/B00KDPI8Z6/
It has a built-in lock, but the "key" isn't unique. It's really just an Allen key, but with 5 points on it instead of 6. Should be good enough to keep small children out of it though, if that's your concern.
I live in an apartment building. My family owns it but I need to keep adults out too, lest they be poking around. I see a few small freezers, that are lockable, and drainable in case something happens to the contents, that get down to -25F or better so I think I'm going to shoot for that for long term storage. Whatever I buy will be based on what I make...so time will tell.