i wold not not not bury it moles dig tunnels and when they encounter they will drag it with them down the tunnel then you precious box will be lost in a maze of tunnels and you will hav to dig your hole garden up to find them.

better create a paper wallet its safer its ink its small its thin it doesnt need electric u can laminate it u can put sellotape over it put it in a jar with dessicant seal it tight and it will last for many years