No method of pressing or preserving leaves is going to allow you to keep them forever. Even the leaves pressed between waxed paper will eventually dry and crumble. If you'd like to prolong your fall leaf masterpieces a bit longer, take a stroll down the floral preservative aisle at your local craft store. There are products for sealing, dipping and polishing. Using one of these gives a little extra longevity to the preserving process.
Of course, there will always be more leaves next year and every year your skill and creatively will only get better.