What kind of pad are you using?
If the pad isn't the culprit in the Sports Saddle slipping, we need to
discuss how the horse is built and/or the rider's position.
I would use a breast collar and/or crupper only as a last resort.
Genie Stewart-Spears
Horse Works
Distributor for the Endurance Sports Saddle
(502) 443-1505 Mon-Fri 9-5 Central Time