The day I bought my first kayak, I had to make several stops on the way home and I realized there was nothing to stop a miscreant from taking it off the roof of my Explorer. After my first paddle, I immediately set out to make it theft resistant.
My idea was that a vinyl clad steel clad cable would be ideal for securing the kayak. This left me with two questions to answer: How do I connect the cable to the kayak, and how to I secure the cable to something?
I looked my kayak over, and then took a look at other models and decided that all kayaks are divided into two groups: those with something permanent to connect the cable to and those without.
My first kayak was a Perception Swifty; the seat was molded out of the same piece of plastic that the hull was. A cable wrapped around the seat support in that type vessel (or through the hull, as would be the case with a sit-on-top) cannot be removed without tearing up the boat or cutting the cable. If you have ever tried it, you know how hard that is.
The other kind of kayak or canoe is manufactured with no way to connect the cable permanently. My second kayak is an Old Town Loon, and the seat mounts to an aluminum rail that is bolted through the plastic hull. Anyone with pliers and a screwdriver can easily unbolt the seat and remove the security cable, so that is not the way we want to approach that situation.