Equi-Essentials offers replacement elastic leg straps for blankets and sheets that already have D rings for attaching them.
Each strap has a swivel bolt snap at each end.. These straps are both adjustable and elasticized.
Leg straps should be fitted correctly for both comfort and safety reasons. Each leg strap should be passed between the legs and back to the D ring on the same side of the blanket. It's important that the leg straps are linked to (threaded through) each other. This gives the blanket the ability to right itself and helps keep it securely in place. You should be able to fit a hands width between the leg strap and the horse's leg so that the straps don't rub or chafe.