Most of the scrappers I see around here either have an overloaded pickup or a roll-back wrecker. Most of the ideas I've heard won't do much to stop either as long as they can drive close. I like the idea of cutting a big enough hole in the beam to thread the chain through, that gets around the whole "welding hardenned chain" thing. Another idea might be to burn/drill a hole through the web or a flange big enough for your lock shackle instead of the chain, and use the lock as the attachment.
I've seen "good" locks fail in short order by people just pounding on the top of the lock with a cheap hammer. On the laminated ones, the rivets fail and the whole thing comes unstacked, so I like the shrouded lock idea--anything to make the lock harder to get at.
"Out of sight, out of mind" tends to help, too. At the very least, make it so it can't be seen from the road. Even better if they can't see your woodpile, as that's reason enough for some folks.
I wouldn't rely on guys being scared to use noisy tools at night, some of them are bold as brass and will work in broad daylight noisy as you please, and just count on neighbors not being nosy.