I would like to add that the ground or track the dog will be working back and forth on should be on the soft side. The dog's pads could be hurt if pulling against this cable set up in hard ground or sand. Can soften it up with tilled in straw and saw dust. With added saw dust to boot.

On the overhead cable you can use old rear end car or truck bearings to slide up and down the cable. Put extra ones on the cable to replace a worn one. A good trolley type roller is great if it will not come off and get stuck on the cable. Cheers