How to resolve a slipping saddle?

don't put more saddle pads down. that will just cause more pressure under the saddle and cause bad habits with the horse. if your riding western i would go to your local tack store and get a breast plate. i would recommend one with cloth on the inside to touch the horse to reduce rubbing. it hooks under the horse on the girth and fastens up on the saddle. they make them for english saddles too. just called martingales. also make sure your stirrups are the same length. sounds crazy but i know plenty of people that don't have them right.