It's like real estate, the three most important things are location, location, and location. A simple cable lock works when my bike is in a shelter in view of three security cameras. Some places, you'll have to remove the front wheel and lock it with the frame and rear wheel, lock your saddle, and take all the lights, saddle bags, and cyclometer with you, and even then it works best if you walk your pit bull to work with you and chain him up with the bike.