I'm going to ask a fairly obvious question, but since I can't see the horse without the saddle I'll ask it anyway. Does the horse have withers? I had a QH who had no withers and it didn't matter what pad you used, thick, think, moderate, if he turned sharp you were going upside down because the saddle would slide right down his side. Solved the problem with a breast collar. It still slipped a little bit but couldn't slide all wht way down his side because the collar restricted the movement.