It's not uncommon to have older folks stash money around the house, whether or not they trust banks. My grandad stashed money all over their little house. My grandma used wait until her purse was too heavy with coins to carry, then put it in the back of the armoire and get a new purse. Needless to say, when my grandparents ended up in the hospital at the same time, my Dad and sister had a frantic time searching high and low all over the house, luckily before the local burglars hit it while they were out. The burglars got some kitchen appliances, but not the money. And my grandparents HAD accounts at the bank, they just....stashed it.

Basically, you have two problems - the safety of the money, and the safety of your father. The money can be put in fireproof bags and stashed somewhere safe-ish around the house. But, again, burglars. God forbid he goes fishing one day and the local criminals loot the place.

Unless you can convince him to take it to the local bank, I suspect that converting it to precious metals and putting that in a fireproof safe, secured firmly somewhere ridiculous, may be the way to go, as it's sort of the go to for preppers. Lord knows my brother in law has gone down that rabbit hole a time or two. But even then a determined burglar is going to walk off with that.