First of all I found this slightly older thread by searching for a whole community on deerskin, if it would exist, because I love it so.. Haha.
Anyway, 1st of all don't put anything on deerskin that has ANY oils in it. It will darken the leather.
Secondly, there is no need to treat for water, deerskin does just fine in water.
Third. I read that there is really no need to treat deerskin with anything.
I DO know that it stays just as soft for at least years. I've had the same deerskin for about 2 and it feels the same as when I got it.
(It's actually a hide that I haven't finished using (sewing with) yet, don't actually have a Prada in it or anything. Just saying cos that sounded weird.)