Well, then you’re pretty much out of luck because if someone wants to steal your bike, they will, even if it means coming with a rotary saw. And yes, it does happen, depening on the value of the bike.
My tip coming from a big city with a shitton of bikes: just get a cheap second hand bike that no one will bother with stealing. If you use it for your commute, then it’s good enough.
If we’re talking about an expensive sports bike, then don’t leave it unattended.