A paper-only journal would defend against the state, but not against people you live with. A digital journal can be encrypted, but an intelligence agency could potentially gain access (like, them reading your anti-government rants that may involve violence… that sort of stuff).
So… how to defend against both threats?
(Also, I just realized, paper journals cannot really be easily backed up…)
A physical journal written in a secret code
This was my first thought as well. The code doesn’t even have to be very secretive to beat most people from figuring it out. Torture would be the only way and it still would have plausible deniability.
So eventually no decipherable, nor understandable decryption easily succeeds. (The previous sentence has a secret message.)