I have only had this problem of slipping skewers once and it was because I had had my frame painted and didnt notice the painter...who did a terrible job generally...had painted over the dropouts. Once I scraped off the paint, all was well. While this does not seem to be an issue for OP, in addition to agreeing that modern internal cam skewer should solve the issue, I would suggest giving some love to the dropouts, making sure they are clean and free of matter that might be inhibiting skewer engagement.