Sewing sequins on

[GiveMeStrength2day]

I've been trying to jazz up one of DD's tops by sewing on a scattering of sequins. I've used strong thread doubled-up. I come through the back of the top (leaving a small "tail") then thread the sequin on at the front then push the needle back inside (slack enough that the sequin lies flat). I then tie the tail and the rest of the thread into a treble knot then snip the ends. I've now noticed (even before I've finished doing the top) that the knots appear to be untying themselves leaving the sequins hanging on by two loose ends!

The material of the top wouldn't take fabric glue. What am I doing wrong?

I find using very small beads to hold on the sequins is a lot easier.

How do you secure the thread at the back though. I understand the concept of using a tiny bead on the front of the sequin but once the thread has gone back through, this is where I'm having problems. Is it a case of having to "cast off" the same way as you'd sew a button on (if that makes sense)? I thought what I was doing was simpler - although if the thread is managing to unknot itself it's clearly not the right way of doing it!

maybe it's your not that is not secure, try this, hold short end of thread in l hand put thread and needle over and through short thread twice and pull tight, then hold needle thread in l hand and pull short thread over and through and pull tight, this should lock the knot so the thread will break before the knot does. sorry a bit of a mouth full but the only way I can think of explaining .

I'm treble knotting the thread. If you can imagine the two ends of the thread being like how you'd knot shoelaces with the sequin on the outside of the material being the "shoe". Then rather than making a bow, I'm knotting 3 times.
cheese - I'm struggling to get my head round your method

Off to Youtube knot tying - I wouldn't be able to learn from pictures

if it helps give me strength its a surgical suture!