I've never been a big fan of using the safety loop you describe. If I fall while walking through the brush I want to be able to toss the machete aside so I don't skewer myself. To improve the grip on my machete (cheap military surplus with a plastic handle) I applied several coats of tool dip - don't know what it's really called but it's the liquid rubber coating used for tool handles. Even when it's poring rain outside the grip won't slip and the rubber layers help cushion as well. A little bit of pine pitch added just helps the grip that much more.