No need to back the Hack, so long as the back is in good condition. Hacks weakness is in it's compression, not it's tension. I didn't see the divot you mentioned, but if the back is dinged up and you need to put rawhide on it then do as DC mentioned. Get the tips lined up and all the heat treating done in one session. You lose too much progress otherwise. Get it bending well before the rawhide is applied. Not enough for it to come apart, but so far as you can safely go.