I have one kilt with no under apron strap. Its a 16 oz wool box pleat and a length of nylon webbing was used for the single strap and buckle to attach to and the top band that covers the very top of the kilt comes all the way down to just cover the webbing. It has no other liner and maybe due to the wool on wool at the waistline it never slips down. I did it this way as it is a nice light hiking kilt (sub 2lbs), 5-10 miles of hiking and hill climbing has been comfortable.