Beautiful work there, that is a lovely mount and you can imagine the long hours spent on it. Once started, you can't just walk away when you get tired. You're committed to finishing.
My PH friends in Namibia get a couple permits every year for both Namibia and South Africa, and it is surprising how many people want life-size mounts of the big guys. As far as the hide, rhino-ele-hippo are all very thick and giraffe is too. A green giraffe hide is just about 2 inches! Looks like watermelon rind, and all that white hide is what is all carved off until it is about 1/4" thick. Then the entire hide is siped about 1/8" deep every 1/8" across to get the salt into the crevices and dry the hair folicles. After it gets to the tannery, they shave it and try for a uniform thickness of 1/8 to 3/16".