Try wrapping the metal part with tape or vet wrap if that's what's rubbing the hair off?
For the chest, both of my dachshunds have it to varying degrees. Sadie is bald there, Fynn is thinning. Both are from rubbing the hair off while laying down, dragging themselves along the carpet as they play and hitting their chests on the stairs when they run up (Sadie more so). I tried putting Sadie in a sweater or wrapping her chest with vet wrap when she was younger, didn't really help, so I just gave up.