I have used Scotchguard on lambskin & it turned out wonderfully. The Chanel at Wynn actually uses Scotchguard after you buy a bag, if you want them to.
You can do it yourself ( I have done it), you just need to use a very light hand on the spray, hold the spray back about 12 inches, and use a sweeping motion.
I watched the SA at Chanel Wynn do it, she put the bag upside down over a rack, and used a continuous sweeping motion. If you can picture using hairspray on a beehive hairdo, it was a bit like that *L*