Chains do not work. They are far too easy to defeat. The same goes for cables. I have a set of bolt cutters with 14inch handles, they could fit inside a jacket, and they could cut most cables out there. Ulocks are much safer. Yes, you can jack them, but jacks are a lot harder to transport about, and you have to be able to wangle the jack between the u and the lock. Don't get a bic-pickable lock, get a real key. Kryptonite sells one - New York Fahgettaboudit® U-lock. They are expensive, but still cost less than $100.00, and unless the bike thief carries nitro around with him/her/it, pretty much will prevent the theft.