Whenever I play on servers, I hide my chests 1 block under a door or bed, nobody ever seems to check there and usually they can't be broken depending on the server
I usually make a lava pit with water right underneath it. It's a pretty good technique and like misterchees0 said no one is going to jump in for no reason. If I'm really bored and feeling a little eccentric I will make 20 garbage disposals and only one of them leads to the treasure.
I usually hide most of my valuables and goodies deep in my basement behind a painting. If you did not know you can walk through paintings, so I think it is a good spot. I usually hide anything else of value outside in a random place under the ground, where no one will find it.
I usually hide my stuff a couple blocks down under a floor, or even over pressure plates or other furniture that I intentionally place to conceal it. This makes it necessary to create side tunnels to access your stuff, which I also have to hide, or the hole will be obvious. Sometimes I will just destroy what's in my way, if I am feeling lazy and need my "goodies" quick.
Dig a hole, then place a chest and dump everything in it! That usually works... until someone digs it right back up.
I usually make some kind of a secret tunnel with wrong turns and traps to get to a cool treasure room. Kind of like an Egyptian pyramid except for underground. I think they're more fun that fooling around with red stone and hard-to-enter alternatives.
I leave it out in the open. I play in a whitelisted server so I know mostly everyone in the server except a few new recruits. My house is especially hard to find since my nether tunnel is hidden and I live extremely far away so you basically have to take a 5 minute minecart trail to reach my house. If someone does steal anything though, I always have my important valuables in my enderchest.
I usually hide my really "good" stuff a couple of feet from my house. Reason for that is because some people will just go to your house and destroy everything looking for the good stuff. So i just go out a couple of feet from my house and dig underground and put my stuff in a chest there
I usually play in single player, so I don't try to hide my chests. But when I actually do play online, I always make it a priority to get Obsidian and an eye of ender so I can hide my good stuff in an Ender Chest, which is the safest form of hiding goodies. Other than that, I keep goodies on me and hide away from griefing players, just in case.
Personally my goodies are under my bed. I usually use large chest and the bed is actually really easy to replace so it makes a great medium for hiding things and quickly replacing the bed! Oh, and the "behind the painting on the wall trick" mete fails either!
Oh I love the painting on the wall trick! I made so many secret entrances to huge open areas of my bases in places like that. I usually lived in cave-homes so expansion like that was easy.
I would usually hide all my valuables in the middle of the ocean! I would literally stay on my boat going out to sea for over 10 minutes just to get to an isolated spot. I would then hide it under 5-10 blocks and then take down the coordinates for later use. Of course, I went through all that effort to hide my things because the server had over 100 people online at once, therefore needing to guard my items much better.
I really like hiding things Paintings and stuff because that's such an inconspicuous thing to do. No one suspects what you've done, and if you have a large hall of nothing but paintings, only you will know which painting your goodies are behind.
I've done this in the past but it has never fooled anyone. Even with a complete wall of paintings its actually pretty easy to spot potential door ways. Where do I hide my treasures? I usually build a long tunnel away from my main base that leads to a treasure room. I then put all my stuff in a hidden nook at the start of the tunnel (opposite end of the treasure room) and make it so the treasure room looks like someone has already broken into it. People think I've already had my stuff stolen so they don't think to keep looking.
When I was playing Minecraft, I did not have any problem to hide my stuff. My houses or rooms were small. All I needed were about 3 pieces of redstone, 4/5 blocks of material which I used to build home and some buttons. It's pretty simple idea. You can do it even under your bed. People aren't usually destroy their beds, right?
I use a complex sticky piston array and a BUD switch to make an invisible trigger for the pistons. The pistons retract and pull up inside the wall to reveal the chests, making what looked like it was a bare wall, a wall of chests. It is quite resource intensive as there is quite a bit of redstone and sticky pistons, although I have tried my best to make the redstone compact and I think I have reached the limit in that respect.
When I build my house I usually hide my good stuff under my house. Like, I would leave a 1 block space under my house, and just drop my good stuff in there.
Generally deep underground a little ways away from my base. Most players like to ransack the base trying to look for something. It's fun creating false hiding spots to throw them off as well.
I love making secret doors with paintings but that's a little stereotypical to do. Ender chests are definitely the best way, they're like a minecraft cloud. I also have done the chest below a tree trick, though, that works very well.
Sometimes I put coal ore around the chests, so that they're completely hidden from any xray detection.
