I had a quilt with tons of threads to be hidden when I got done. I bought one of those cheap needle threaders--the one with a bent wire to pull the thread through the eye of the needle and buried each thread after knotting them on the back. Worked great and didn't take a lot of extra time. At the beginning and end of each row of stitching I sewed a couple of stitches very close together. I didn't want to backstitch since that would show. As far as I know the stitching has held up wonderfully--at least I haven't had any complaints.
Sue