If you want something simple yet bomb proof for thicker, stiffer lines, this is one I picked up in the States years ago, no idea what it is called but it has never let me down. rather than try to explain it, I found this vid and it describes it perfectly.
That is an interesting bit of kit. I’ve certainly never seen it before. However is it really needed? If you have troubles with that knot slipping then maybe it’s not been tied properly or you need a different knot?
Yes the palomar knot, Great White is spot on, probably the simplest knot to tie and also one of the strongest, the double palomar is about 15% stronger but slightly bulkier.