Buy jewelry, gold and silver coins, gemstones, rolls of silk, fine pelts, expensive spices like vanilla beans (avoid saffron though, its perishable), fine porcelains and maybe a rare painting or two. Put it all in a big wooden chest with a big iron padlock on it, and bury it in your backyard. Then draw some sort of cryptic map to it in case you die unexpectedly, or forget where your backyard is or something.
Also traps, lots of traps - something fancy like blowpipes shooting darts when an intruder steps on the wrong stone of a floor puzzle, maybe even a large an perfectly spherical stone that rolls towards intruders if the weight of your chest is altered.
There's a series of documentaries about such things were a professor of Archeology - a Dr. Jones, if I'm not mistaken - illustrates their workings.