One of my friends in university used to patch her jeans from the inside by glueing pieces of denim directly to the cloth as soon as they
started to fray. It wasn't visible, it meant the the tears didn't grow as quickly, and when the jeans were no longer usable, she saved the cloth to patch her next pair.
She was outrageously hot and had the confidence to carry off pretty much any outfit, but I honestly thought it was a good solution.