Well all i can say is that every time my bike was stolen it was locked with a heavy duty chain, or in a locked basement, or in a locked cage-room in the basment so the thieves have no chill. My biggest mistake was probably that it wasnt locked to an immovable solid pole in the ground but you cannot always find that whereever you need to park, and a thin bikerack that is the only thing you can find in the city is so easy to cut open for thieves that they'll cut that instead of the lock so no lock will help here either. Thieves are lazy so making it look like it'll take hours to make the bike resellable is the only true option together with a heavy duty chain like the abus city chain x-plus