A good lock is one part of the equation. You also need to lock your bike securely.
Lock your bike to an uncuttable, immovable object in a well-lit, high-traffic area.
Lock your frame to the immovable object so that the lock is accessible for you, but difficult for thieves to manipulate. Bike Winnipeg recommends locking your bike through both the frame and your rear wheel.
Choose an immovable object that cannot be broken or cut, or dismantled so that your locked bike could be lifted off the rack. Never lock to a tree or a chain link fence.
In addition to locking your frame, secure any important parts of the bike that a thief could easily remove, like wheels or the seat. On the one hand, you could set up your city bike so that neither the seat nor the wheels are easily removable. On the other hand, you could secure the rear wheel and the frame with your Ubolt lock, use a cable to secure the front wheel, and bring the seat as well as any easily removable accessories (lights) with you.
Keep in mind that it is common for thieves to steal the frame of one bike that has only been locked through the front wheel, and the front wheel of another bike. Never lock your bike just through the front wheel. Also, it is common for thieves to steal the seat and other important parts from a bike, hoping that the owner will abandon the bike overnight, so that the thief can come back with a grinder to cut the Ubolt.
Lock your bike properly at home too. Many bikes are stolen from garages, where they have been stored without a secure lock. Set up a secure lock-up at home; do not assume that a locked garage is safe.