I knot certain yarns (like the much-maligned Homespun, lol!) and then weave in really long ends back and forth and haven't had any come loose (knock on wood!). My DMom made an afghan for my DS, out of said LB Homespun, and it literally fell apart and bless her heart she re-did the whole thing (such patience she has! I would've thrown it out, lol). She had woven the ends the traditional way, but in the end she used knots and weaving in to be doubly sure and it has held up for years now.
I generally don't knot except to temporarily hold ends for future weaving in, but I also knit a few stitches together first and weave in in two directions for a really long way.
The hole in the hat is heart-breaking!! It's such a nice hat, too-love the cables! Oh well~at least it is probably a lesson that won't be forgotten