The first issue in bicycle security against theft is what kind of bicycle you are locking up. A bicycle that looks like a junker can ride like a dream. An older frame with scratched and chipped paint and nice but undistinguished-looking components is a good choice. Let it get dirty. Sheldon's Mead Ranger is a good example. That's the original paint, or what's left of it. This bicycle is really old. (1916! -- maybe too old, it's collectible, but most thieves wouldn't understand such subtleties. In any case, this isn't a daily ride-to-work bike.)

If you don't have secure parking at your workplace, or will be locking your bicycle in unsecured areas, you should have a serious lock, such as a Kryptonite. You need not carry it home every night unless you also are locking the bicycle in high-crime areas on the way home. The weight of a typical U-lock represents the difference between a $400 bike and a $1000 bike.

People tend to buy big, clunky U-locks because they don't know how to use them properly. A U-lock can go around the rear rim and tire, somewhere inside the rear triangle of the frame without looping it around the seat tube: the wheel cannot be pulled through the rear triangle. A lock which passes around a rim makes the bicycle unrideable even if the object it is locked to can be broken or disassembled.

The best U-locks, if you must carry one on the bike, are the smallest. The Kryptonite Mini is much smaller and lighter than the more popular models, but just as secure. It may be even more secure, because of the limited room to put an automotive jack inside it. It also gives less purchase for leverage-based attacks.

Some will object that felons might cut the rear rim and tire to remove a lock. This just doesn't happen in the real world. It is possible to cut the rim with a hacksaw, working from the outside to the inside, but first, the tire must be removed or cut through. It would be a lot of work to steal a frame without a usable rear wheel, the most expensive part of a bike after the frame.

On the other hand, a slightly longer lock would fit around the rim, and the chainstays or seatstays...or locking from the left side might allow a smaller lock because the chain doesn't get in the way...you might need a longer lock too, for when you can't get the bike as close to a pole.

Lock the bicycle in one way or another, or at the very least disable it, whenever it is out of your sight. Theft can occur at unexpected times and places. John had his bicycle parked in the fenced-in back yard of a friend's house when it a guest who left a Thanksgiving dinner early rode away on it. A general invitation had been issued to people who attended the same church. This person evidently did not subscribe to the teachings of the church. A simple cable lock would have prevented this theft, and there was one in the bicycle's touring bag...

Some workplaces have secure bicycle parking. You may be able to take the bicycle inside your workplace, or there may be a secured parking area. The bike cage shown in the photos below is next to the parking-garage entrance at the Dana Farber Cancer Institute in Boston. The entrance is under video surveillance and the door has an electrically-operated lock. Employees enter by swiping a smart card; others must press a button to speak over an intercom with a guard who releases the door. Still, lock the bicycle and remove valuable items.

Lacking this level of security, you can leave a heavy lock at work, locked to whatever you normally lock your bike to. Carry a light cable lock with you for quick errands or emergencies. It is easily cut, but you are making a trade-off between security and convenience.

If you must lock your bike in an unsecured area, choose an area exposed to public view if possible. You may be able to lock your bike in a praking garage in view of the attendant.

If you use both the U-lock and the cable lock, you are more than twice as safe as you would be with either of them alone. Either type of lock can be defeated, but each requires a different large, bulky tool which is useless against the other.

The cable lock will secure your front wheel to the frame and any convenient object, and the U-lock will secure the rear wheel and frame. If you have a quick-release seatpost bolt, replace it with an Allen-head bolt, put a cheap saddle on your commute bike, and then you won't worry.

The best cable locks have the lock built-in, rather than relying on a padlock. The padlock is the weak link, easily cut with bolt cutters, the tool of choice for most bike thieves. A new, sharp bolt cutter will cut a cable too, but an old, worn-out one will only crush a cable.

Lock to an object which would be difficult to cut or disassemble, and where the bicycle can't be lifted over the top. Good, secure bicycle racks are becoming common these days: "dishdrainer", wheel-bending racks are seen less often. A thick signpost, cast-iron fencepost, parking meter post etc. is good, as long as locking there is legal: bicycles also may be removed by police and maintenance crews. Check before locking: some posts can be lifted out of the ground, and thieves have been known to cut bicycle racks, taping over the cuts to hide them. If you are stuck with a dishdrainer rack, lock to the end of it if you can. If one is in a secure area, back the bicycle in:: the rear wheel, unlike the front, will hold the bicycle steady. Lock the rear wheel to the rack and the frame to the wheel for additional security.

Face the keyhole of your lock down, so water doesn't run into it. Some locks have sliding covers for the combination dials or keyhole.