Sadly, I live in a very high-theft area so there are no ironclad solutions. Their preferred method is to cut the frame in two at the top and downtubes using an angle grinder (or hacksaw if noise is a problem but time is not) and take both halves away to harvest the components at leisure in casual "chop-shops", in most cases homeless camps by the river. Parts are not serially numbered like frames and can be turned quickly on Craigslist (our Gumtree), via eBay or in person. Top and downtubes are only about 0.5-0.6mm between the butts, so it doesn't take long to get through them.
It is hard to guard against such no matter what lock you use. On my daily 8km walk today, I spotted another four frame "halves", stripped of parts. In a sweep by the parks department a couple years ago, over 350 frames were recovered from one smallish park area off the bike path.
Best approach is to avoid physically leaving your bike unless it is locked inside a secure location where parts cannot be harvested off it. When traveling, I have found it helpful to ask if I can lock my bike at an attended petrol station while shopping for groceries nearby, offering to bring the operator a coffee and pastry on my return. It has worked out well.
Another method sometimes used by thieves here is the "grab and go", where bikes next to where one is standing are grabbed and ridden away while the owner is either taking a photo, changing a jacket or pushed to the ground. For any casual stop like this, I use my frame-mounted ring-lock. It is always with me so I can't forget and I chose the kind that retains the key while unlocked, so I won't forget the key at home. I use a coiled wrist band and clip to keep it with me off the bike.
I use a ring-lock on several of my bikes with a choice of plug-in cable or light or heavy chain, depending on circumstances. The saddle gets its own cable, secured through the bolt of the ring-lock and this also threads through my underseat bag. The ring-lock cable secures the anti-theft tethers on my Ortlieb panniers. The handlebar bag always, always, always goes with me so I don't even take a key for its locking mount. I also have a remote controlled motion-sensing alarm under each bike's saddle.
Whenever I stop to use a public toilet, I bring the bike in with me...and lock it while I take care of business. I carry a small rubber doorstop so the spring-actuated outside door won't catch the rear mudguard on the way in or out. Also handy if you're stowing or recovering your bike from a cloak/storage room or concierge closet at formal lodging.
So far -- using care! -- I have not had a bike stolen, but it has come close with my Nomad as a thief tried unsuccessfully to run away with it while the ring-lock was secured and the plug-in cable wrapped 'round a picnic table bench. I was glad I had taken the precaution, especially as it happened while I was seated eating my lunch at the other side of the table(!). Apparently he didn't notice the ring-lock or the cable, which was plugged in and secured on the other side of the bike. Moments before, the thief appeared to be just a guy in the park, pausing momentarily by my table to check his cellphone. They're bold, our local thieves.
Best,
Dan.
