An outlay of a few silver coins gets you a good leather skin, which you slice into a series of squares. Being originally part of an animal, it would theoretically retain magical energies better than most, and would retain the connection between the squares as they were once part of the same animal. Using reflected and concentrated sunlight, you slowly and carefully burn the appropriate sigils into each piece, doing your best to ignore the smell.
You need to put the pieces aside and work out on paper the correct way to divide the spell up so it can be split between different squares and still combine back together, which takes days of work as you convert the spell to thamaturgic equations and then try to find the best way to split it, and then convert the divided fragments back into pieces of incomplete spellcraft which then have to be made into enchantment, but you're unable to find a way to make an enchantment both self-contained and fragmented, so you have to go back to the beginning and convert the process of enchantment into thaumaturgic equations so you can derive that into fragments. By the time it's complete you're wondering whether the holding-the-robes-immobile thing would have been easier, but you press on.
Each of the squares of leather, when enchanted, is magically useless; it's only in combination with the 15 other leather squares and the 15 other fragments of the enchantment that they combine to form a working piece of magic. Or so the theory goes, and you've no way to check whether it works until all sixteen pieces are enchanted, and each square is a full day's work in itself. A week passes, then another, and finally you've got the end result ready for testing. You impatiently sew each of the squares into place in the lining of your robes and then wear them, feeling the unfamiliar weight they add to your usually so familiar robes. Then you press down on the square of leather on your left hip, and the familiar grey sinks into inky black as shadow rises from the weave of the fabric and spreads over your exposed skin. An experimental knife-cut on a sleeve fails to penetrate it, and then another on your palm similarly fails to cut, and you smile.