It's hard to tell the strength from that picture - are those hand-made knots? They will need untying or things will get caught up as everything tightens up - assuming you're putting one end through the handle to form a loop. I've considered the dog lead in the past and didn't trust the metal end to hold. That being said, I've always had leads with really good stitching on the handles. Perhaps consider bed sheet material in a long strip.
As bizarre as this sounds, I once had a short-lived addiction to the high of partial hanging, maybe someone out there knows what I'm talking about. I always found the knot of the noose at the front most effective, at the back it was just choking me. Your head is basically looking up. I was in a position to release the 'rope' at any time, whether it was by choice or passing out - which happened a couple of times.