One of the most ancient known tan material is dried(until it become white) dogshit.
According to my research via wiki and books, it tan hides faster(and were pretty valuable) than bark or rot, and take less amount to create tanning fluid. The problem is it's need to be properly dried, thats why was abandoned through time.
Guess would be fine addition if dogs sometimes will be implemented, but for now could be fun to find wolfshit at mountains.
P.S. iin addition wolfshit could be used to make a simple repellent to make wolfs less aggresive to heartling for some time.