If you are getting 'bulges' at the edges then you need stiffer poles. The edges are stretching because the poles are bowing or deflecting. You can buy a spinner as suggested - not a bad idea - and it will reduce the weight of the rugs being hung, thus possibly solving the problem. The cheaper, and more certain, solution is install stronger poles. Plastic sleeves are a nice but they won't solve the problem is your poles are not flat under load.