You can't tie a clove in a limp wristed wishwashy fashion and expect it to be OK. It had to be set tight with the two half hitches snug against the crossovers. The halfhitches are to finish the knot, they shouldn't be thought of merely as backup. The near mid-tie in the video pulls the knot against the wood, as opposed to down it. It not through luck or chance that we've never lost any that way.
Way back in '76, I'd only been doing tree work for a year, when, while running rigging for my crew foreman Darrel, I watched his clove hitched piece roll out, as it tipped over, the knot held just long enough for the load to swing past the house. It may have brushed it, but did no damage to the roof or gutter. Ever since then, I've always tied cloves properly, with two half hitches, which are an integral part of the knot, not just a back-up, as you said, Reg.
Edit, just read this whole thread, which turned into a disaster confessional, to see that August made the same mistake, only with consequences that were not so lucky as Darrel's screw up. Mind you, I'm pretty sure Darrel didn't add even one half hitch to the clove.....
I could add a mess of my own screw up stories...but still have images to edit from my weekend... and overdue biz paperwork to finish up.
Great work, naturally, Reg. I'm gonna get a couple of those new fangled toys you were using, fo sho!!