I have the primos sling that goes over the cams and string. Its great for carrying around at 3D shoots or anywhere else that you don't need to shoot it.
I've seen a few at shoots that attach to the top and bottom of the riser and have a buckle that snaps on/off. You can shoot with them on, but they are pretty slick to take off. I don't know who makes them, but they'd be better than the one that I have.