Diversity is good. At home you use clever concealment, like the in-wall idea someone posted, and the fake pipes idea I've seen on YouTube. You just add a fake pipe or two under a sink, in have coins or rounds in the pipes like in any other tube – perfect fit.
Buried is good too, with some constraints on how quickly and easily you can retrieve buried stashes, depending on distance, depth, privacy of location, etc. I don't believe in SHTF nonsense re: silver because almost no one owns any silver or other PM, therefore it can't be widely used as money or barter in a crisis. People can't use what they don't have. So I don't think you'd necessarily need to retrieve your buried treasure super quickly because of a social collapse.
Bank safe deposit box is also good. People have noted the third-party risk. That's just a mundane risk like any other risk, and needs to be quantified like any other risk. What's the probability that you'd lose your SDB contents? Well, how would you lose it? Probably either a major, sophisticated bank robbery, or some sort of government seizure that some PM enthusiasts worry about. The probability of a (non-governmental) criminal heist is extremely low. The tunnel heists are rare enough to have their own Wikipedia articles. They happen, what, less than once per decade in a country as large as the US? Once every 25 years? Or even less frequently? How often do they happen in Oz?
The non-tunnel heists I'm not sure about. A bank robbery these days is usually small-time drug addicts or something who quickly get cash from a single teller and flee. The well organized stuff you see in movies seems extremely rare now. I'm not sure how rare though. And most of those jobs don't bother with the SDBs – they're focused on the cash only. The SDBs probably have a much lower payout per second spent in the bank. They'd be dealing with lots of birth certificates, passports, personal effects, legal documents, jewelry of varying value, some cash, some PMs, and even completely empty boxes.
This compared to the amount of vault cash they could shovel into their bags in the same amount of time. Seems like they'd have to see SDBs as a waste of time that would reduce their total payout. SDB robbery makes more sense for tunnel jobs where they can take their time, say over a weekend when the bank is closed. And especially if they already know of something in a box that they specifically want, like an extremely valuable work of art or other object.
So it seems like SDB are pretty safe. I would diversify storage to include all these methods.