My primary defense is the lock it inside limited access bike rooms - I have my own spot in a bike shed that only people paying for a bike parking spot can access at my home, and at work there's a bike room that requires a badge to access.

Additionally, I have a folding lock that I fold around some kind of secure piece of metal, through the frame and the back wheel.

When out and about, I try to leave the bike where I am able to see it, in daylight, in places where there's a good amount of foot traffic.

These strategies have worked out so far. I'm considering upgrading to a U-lock, but I've so far been reluctant as I fear it may reduce the amount of places where I can lock the bike to.