I don't have a saddle slipping forward problem 90% of the time. A couple times, I've ridden my horse's neck. Once, I was doing a ride in the Alabama mountains (who knew?) The last two miles were over "Yahoo Mountain", which you went up sharply and than back down gradually. After about 10 minutes of walking down hill, I realized my horse has really cute little ears and -- hey, why is her neck so short?
I was riding the poor mare's neck and she was kind enough to stop before it got too bad. I had to get off and reset my saddle before finishing the trail.