About two months back I broke my standard pattern of three girth checks before mounting (one when the saddle is placed; a second when we get to the ring; a third just before mounting; I keep my right stirrup up until I do the third check but on that day I'd lowered it to reset the length and didn't put it back). I got up without difficulty and worked for 20 min. Or so until the instructor got out there. As soon as saw me she started to laugh. When I asked her what was so funny she walked up and put her fist between the girth and horse's belly. Oops.
We took out the slack and the lesson commenced. Three lessons to be learned: don't break your patterns; ride the center of your horse; send a nice note to Stubben thanking them for a well designed saddle.
Several years ago in Western Horseman
there was a story written by a guy who was drafted in 1941 and ended up in a Cavalry Training Company at Ft. Riley, KS. His CO was an older captain who was very gaunt and dour and was nicknamed "The Skull."
About half way through basic they were riding back to garrison. With about 2 miles to go The Skull stopped the column and told everyone to remove their girths (they were riding McClellan saddles). He then moved the column forward at the walk then the trot then the slow gallop and then the charge. When they arrived home there were 4 men left mounted of the 100 who started. They each got a weekend pass.
There are several morals to this story but one is that good fit and good horsemanship will keep the rider where they belong.
Again, if a saddle does not fit adding pads, breast collars, tight girths, etc. will not solve the problem.