Buy a breast collar and properly fit it to the horse. I attached a breast collar to my barrel saddle and I never had a problem with saddle slippage. if there was any, it was minute.
I'm not familiar with endurance saddles, you will probably need to find an english style breast collar, rather than a western style.
Add your question to the trail forum if you don't get a more detailed response soon.
I wouldn't use cord or any jerry-rigged solutions. you have a greater potential in rubbing your horse wrong and causing a sore. Whatever you attach to your saddle to keep it from slipping needs to be supported via the neck and shoulder muscles.
it has to go around the horse. western are the best because they generally have a larger width of leather to dissipate the pull of the saddle (with you on it) against the horse going up hill.
avoid the thick fuzzy ones, they never lay flat. and look for a collar that has an attachment to the saddle and to the girth. the girth attachment keeps the collar from rising up.
Last edited by AQHSam; 09-21-2013 at 08:55 AM.