VA,
Well there's a lot of help and agreement coming your way! Just want to backup Bigame's note that it sometimes takes a couple/few tries to get the tension right. Mine stay put when they should, and move when I move 'em - but I didn't get that on the first try.
I'm thinking you've got plenty of knot suggestions to draw from. To name some that'll work: constrictor or double constrictor, clove hitch, nail knot… With the constrictor or clove hitch, I always tie a square knot or two (opposite side of where the first knot ties off). I think just overhands , alternating sides, with a square knot finish would probably work. More about the tension than the type of knot. Also, do cut the tag ends short and carefully melt 'em, and press the melted tie material into the knot as soon as you blow it out.
Just get 2 or 3 sets so you don't have to worry about getting it perfect the first time. And think about finding a cut off saw, like stagetek suggests. You don't really want to bring your business back to that shop, do ya?