The furler line is only secured by a cam cleat (under dodger flap in shadow) on our J/109, so when leaving the boat we clove hitch it around the winch. Also note the sheet is half hitched around the standing part.
Before leaving the boat we also make very sure the jib is neatly rolled and the sheets take a couple of tight turns around the clew.
Unintended jib unfurls are common and a seamanship fail.
I like to also tie a sail tie around the sail where the sheets are. Then even if the furling line was to break the sail would not open up.
After seeing the destruction caused by unintended unfurling due to a gale, and to maximize the life of my genoas, I generally drop and bag the sail if I’m going to leave the boat unattended for more than a week or two. Our boat is currently in a slip in Ventura, CA, and we live ~900 miles North of that. A boat neighbor in Ventura reported seeing over 50 kts in the harbor this week, and he counted 10 jibs that unfurled. I’m really glad we left our boat bare headed!
I agree: https://www.morganscloud.com/2009/09/01/gale-and-storm-preparation/
Agree with Edward. Wrap a sail tie around the jib itself on the forestay and sleep well.
The boat beside me in our yard had its furled sail on until I reported it to the office. The owner of the C&C 27 Mk. 5 in question were new and didn’t know to take it down. But with the wind we get, it was a menace in waiting.
It has not been the only boat cradled with sails still on there.
When the boat is left in the marina, we tie the roller furling genoa tack shackle tightly to the bow pulpit to back up the furling line. During hurricane season when we can not immediately return to the boat in its marina, the canvas is stripped.
We do the exact same thing every time we are done sailing for the day even when we are sleeping aboard. Our clews are too high off the deck to easily reach them to secure a line around them. Removing the furling line safeties is on our predeparture checklist.