Here is a long thread in which many ideas for hiding money were discussed. The thread is a mix of humorous and and serious. You might enjoy it.
Where Is the Best Place To Hide Money In Your House?
May I also suggest that you can put money directly into a
safe deposit box at a bank? Credit unions may have them, too. A safe deposit box is a box to which o
nly you have a key and it is inside of a huge, walk-in vault that is securely locked at night. The vault is like a room that is lined with locked boxes. Only one customer is allowed into the vault at a time, so you have privacy and security putting your items in or out of your own box. No one asks what you are putting into or taking out of your box: it is totally up to you.
If you have never seen safe deposit boxes and bank vaults, you can go to a bank and tell them you might be interested in renting one and ask if they can show you the area and explain how it works.
At my bank, rental fees for the smallest box is about $20 per year. A safe deposit box is where many people keep important papers they must not lose in a fire, flood, or theft, or misplace. Many people also keep valuable jewelry or other small valuable objects there. You could put cash in there. It would be safe, but a little inconvenient to add to or take from. You can only get to your safe deposit box during regular open hours of the bank. Some banks do not have safe deposit boxes at all branches.