Antelope rawhide is the premium choice for backing. I have backed a few dozen with it and have had nothing but the best of luck. I even backed some poor grade hickory with a lot of run outs and had them hold up!
I used to get them from a guy that advertised in P.A. but he has kinda gone dark in the last few years.
Years back I was laying out the rawhide on a hickory board bow when a friend dropped by with some rando nit-wit. Said nit-wit was full of advice on how I really should be doing this (having never made a bow in his life, he was incredibly confident of his unequaled genius). He was fingering a scrap of dry antelope rawhide that was even thinner than a playing card. He proceeded to tell me that I should back my bows with buffalo rawhide, that's what the Injuns did. I countered him by explaining that the rawhide would be too thick, would add far too much weight and ruin the cast of a good bow. He snorted in contempt and proceeded to tell me that antelope rawhide has no strength. I told him to break the quarter-inch wide strip in his hands and he proceeded to tug on the foot-long strip. When it did not tear like tissue paper he wrapped it tightly around his fingers and before I could stop him he proceeded to give a manly grunt and JERKED hands apart. It bit deep into both pinkies. On one hand, it cut through the skin and meat to the bone, and on the other hand it sawed deep into the first joint. Numbskull proceeds to start shouting and bleeding all over my shop. My buddy refuses to allow him in his new pickup and get blood all over the seats, so I HAD TO DRIVE THE UNINVITED AND UNWELCOME IDIOT TO THE EMERGENCY ROOM! Needless to say, I left him at the door and went home to scrape off the incorrectly set and now half-dried rawhide backing on the limb I was working on.
So, is it tough? I dunno, maybe.
