The Clock Stash
A secret compartment that is hidden in plain sight just don't let others change the battery.
Getting In
Take off the back plate that covers the battery and mechanism
Stashing the Loot
Now take what ever you want to hade from others and put it inside the clock. If you prefer you can even build a compartment or box to put in the clock.
Hide
Now replace the back plate and put up in the mantel or shelf.