: On my Hybrid Cormorant, I built a retractable skeg whose mechanism
: was a stiff stainless steel wire running in a tube from the skeg to
: a sliding control next to the cockpit. This is the same sort of design
: used by Valley and North Shore (and no doubt other commercial kayak
: builders). Its neat, reliable, but a bit of an effort to build, and
: perhaps a little prone to jamming.

Walden uses exactly this system and it works well. VCP uses a cable, as do most other companies.

: I've seen two other methods of deploying a skeg, both relying on bungie
: cord. In one case (Masterlite plastic kids river boat), the bungie pulls
: the skeg down, and a cord and cleat pulls it up, whilst in the other case
: (Nigel Dennis Romany) the bungie pulls the skeg up, whilst the cord and
: cleat pulls it down.

Unless NDK has chaged their rope skeg system, you've got it backwards. The rope pulls the skeg UP. VCP's rope skeg works the same way

: Any thoughts / experience / alternative designs ?

Stick with the wire and slider system. In my experience, they're more reliable and easier to fine-tune that rope skegs.