It has velcro on the backside to attach to the fleece of your western saddle. Two separate pads keep pressure off of the spine.
What do you think of these? Do they seem safe? It looks like the velcro could just slip, and there goes your pad. Getting the pad attached evenly to both sides of the saddle might be a chore as well.
I found them here (they are super expensive, regardless of the lack of material used to create them!):
Hill View Farms proven products for horse and rider saddle PADS for saddles