-- Last Updated: Feb-05-13 10:47 AM EST --
And park under a light, near the door.
Here is a source for cable locks, there are others that have similar ones. Wrap them around everything in sight to be visually confusing.
http://www.lassosecuritycables.com/
Also, just slow the thiefs down with extra straps. Double the straps front and back, both bow and stern tie downs and a couple of cable locks... if it takes them 20 minutes to figure out how to even detach the boats from the racks they'll likely move on.
I am sure you can buy alarm things that will go off if some connection is broken. Or you can just add some objects that will fall down and make a lot of noise if the kayaks are dislodged.
If they are pros looking for certain kayaks, they'll probably get around anything. If it is an opportunity grabs - something that is pretty easy to manage for a lighter boat like the Loon - just making it take time and parking under lights should do it.