Keep them hidden. Or stay around and guard them. No lock will stop them; all locks are trivial to open.
My solution is somewhat different: My bike is so old and funky that nobody wants it! It was a fairly decent mountain bike back in the day (Kona) and still rides great but I've put some silly bmx riser bars on it with the wrong color, covered up the name decals with tape, and added a homemade rear rack. A flimsy cable lock is all I use and no issues yet; had it 15 years now. I don't take it to cities; the thieves may be less discriminating there.