I notice you haven't received any replies to your query, so I thought I'd weigh-in.
I'm not sure what you mean by a "retractable" bike lock, but one that meets that definition is the ring-lock, also called a "nurse's lock" in some places. It fastens to your seatstays and has a retractable steel ring that closes through the spokes to secure the rear wheel. The wheel cannot roll, and it would be hard (but not impossible) to remove the wheel. Some variations allow for a plug-in chain or cable to further secure the bicycle to a post.
A ring-lock alone isn't the ultimate in security, but it is always "there", very convenient, and a person will actually use it. Unlike a bare bike, a loaded touring bike would be pretty heavy to carry any distance, and a plug-in cable or chain makes that more difficult as well. For more urban use (rare: think stops at grocery stores and farm produce stores in the countryside or at a fast-food stand), I can also toss in my U-lock as a supplement, and I have a motion-detecting alarm as well.
If you'd like to read more about ring-locks on the Forum, you can find the informaton here:http://www.thorncycles.co.uk/forums/index.php?topic=4148.0http://www.thorncycles.co.uk/forums/index.php?topic=1944.0
The Abus Amparo and the AXA Defender are the two most popular current models. Both fit Thorn bikes equally well, are equally secure, and each offer a choice of plug-in cables or chains to supplement the ring-lock. A buyer often has the choice to specify a removable key or one that remains in the lock when riding. There are advantages and disasvantages to each, so it is down to preference and need. To see how I attached a ring-lock to my Sherpa and
kept a frame-fit pump, go here: http://www.thorncycles.co.uk/forums/index.php?topic=3896.msg19454#msg19454
Hope this helps.