We own a 14 year old mare with high withers, and had a saddle made just for her, but just like before the saddle will slide back about 4 inches after about 5 min of riding her. We have bought about 4 different pads and still have the same thing happen. Please help someone.
Can you take pictures of where the saddle is sitting when you first saddle her up and then take more pictures of where the saddle ends up after sliding back on her?
A saddle sliding that far can be a sign of a couple of things. One of them is very bad fit, which shouldn't be a problem if the saddle was made for her. The other is perhaps she isn't being saddled with the saddle in the correct placement so, during the course of the ride, it is sliding back to where it should be.
English saddles often slide back if they're too narrow. Saddle-fitters sometimes fit to the angle of muscle behind the shoulder instead of the shoulder itself, specially if the horse has a poorly developed trapezius.
If it is English and you bought the saddle within the last few months, or the problem was apparent straight away, the fitter ought to come back and sort it out. Well, any decent fitter should IMO.