We had the jib off, so I just replaced all the standard Harken shackles our new furler came with with Wichard self-locking ones.
We have been using these things for decades in places where wiring the shackle is not a good idea (spinnakers are expensive) and never had one back out on us. Highly recommended and really nicely made.
That said, on an offshore voyaging boat, I would add a drop of Loctite Blue.
You can see how they work in the closeup below.