How many places will you need to lock up with ultra-high security? I would get an inexpensive chain in addition to what you have and leave the chain where you lock up most.
Universal Cycles -- On Guard Mastiff Chain & Key Padlock - 31" x 10mm
Also consider other human factors - park where lots of people walk. Park where there is a security camera. Park next to someone with a nicer bike and then lock up better than they do.
You don't have to be the fastest zebra in the herd, you just can't be the slowest - What I mean is that you need to make your bike a less attractive target than someone else's.
Big, hefty chains like the Kryptonite are where it's at, but you're right, they're heavy.
Originally Posted by NFD40
Cruise around Manhattan, and you'll see a lot of heavy chains sitting on the ground wrapped around posts. Some people tend to buy multiple chains and leave one at each place they intend to park their bike. Personally, I don't care for this approach. In addition to being expensive, it means that I can't simply decide to go somewhere new on a whim- I'm locked (pun intended) into a certain commute path every day. Though to answer your question- the higher-quality hardened chains tend not to rust at all- just be sure to keep the lock itself clean and well-lubricated.
I carry mine with me. If I'm feeling particularly heroic, I sling it over one shoulder and around my chest like a bandolier. It only weighs 8.5 lbs, and all the cool kids are doing it:
I've also seen a few people wear their chain like a belt around the hips. Protip: if you decide to do this, do not lose the key.
More conveniently, however, I have a wire basket on the rear of the bike, and if it's not filled to capacity, I simply toss the chain into this. If you lack a basket, get one. Not having to wear a backpack on those warm, muggy summer mornings is worth the $30. If you still don't have a basket, you may be able to wrap the chain around your handlebars, or around the forwards triangle, depending on the size.