If it's just about Kemono, it's easy to solve (password protection + share password on Discord). But if someone really wants to leak the game, there isn't a lot of things an indie dev can do.
A basic protection is always welcome to make things harder for a leaker (eg: mass Patreon sharing in Kemono).
But of course, it won't prevent someone to join a Patreon, grab the files, extract and send it to F95 staff (or just share files link + password). And if you're successful, eventually it will happen, for sure.
In the end, I guess the best way to deal with leaks is basically ignoring them. Maybe trying to farm some patrons as well, if possible.