When Brutus arrived in Rhodes and asked for money to pay for the war and eventually forced the population to pay. The inhabitants opened tombs and other hidings to recover their silver and gold, that's how treasures are created (if for some reason the money is never recovered). Rome had some sort of giant gold/silver deposit, the aerarium but it only stored the public treasury, and it was plundered by Caesarians. In addition a wealthy roman can still flee the events by visiting some friends or moving to a more isolated domain he own. Of course the problem of guarding of hiding is a bit the same, as the dominus could not have hidden their gold and silver alone, but some of the (educated) slave (or freed slave still serving him) were really dedicated to their master.