Every few weeks my stirrups feel too long and I have to punch another hole in them. I was wondering if there is a way to fix this or if this is just what leathers do. I don't remember having to punch new holes all the time in my older saddles.
Every pair of stirrup leathers will stretch, actually pretty much anything that's leather will. But every few weeks is a little abnormal? Mine will only stretch a few times in a year, so maybe consider getting a new, better pair?
Switch leathers every few days or so. That way one side wont stretch more then the other. They of course stretch naturally over time. I have synthetic leathers for my synthetic saddle, they of course don't stretch too much. You can also get leathers with webbing inside so they have minimal stretch.
If they are English leathers, don't oil them b/c that makes them stretch. English or western, if they are stretched unevenly you can take them off the saddle and have a saddler cut / reassemble them so they are even again.
As someone has already said DO NOT OIL them, clean them as normal with saddle soap and grease them to keep them in good condition
When you buy a pair of leathers make sure they are a pair, leather is cut from a hide ( or butt ) from the backbone to the belly , the backbone will be stronger and less prone to stretching. A problem with uneven stretching can be caused by one of your leathers coming from the backbone and one from the belly. If the leathers are made properly there should be a number at the point end on the inside - the number is punched in pairs when the leathers are cut , this makes sure that the leathers are a pair when they leave the workshop , so look for a pair that have the same number - they should have been cut from the same place on the hide and therefore should stretch the same.
The other things that are important is how the leathers are made.
Stirrup leathers should always be hand stitched, they should also be made with the grain ( or shiney ) side on the inside , many people think they have been made inside out but this is correct. The grain side is harder wearing than the flesh side - so it is the grain side that you want to come into contact with the stirrup iron and the stirrup bar of the saddle
You can spend the money and buy some really really nice non-stretch ones. I finally got fed up with stupid, stretching leathers and bought some that are high strength nylon in the core with very soft leather on the outside (I'm fairly certain it's lambskin). They are very difficult to stretch, but they will stretch out if you are jumping (although not much - and only when you are first using them). For dressage, they will probably never stretch enough to be noticeable.
They're around $150 new, I got a pair that were hardly used for around $75 from a friend.