I have torn rotocuffs at least three times. Two of which were badly enough that I figured my shotgun/rifle shooting days were over and it took over a year of painful, careful, diligent rehab work to recover some. I no longer have the strength and speed I used to have so bird hunting is frustrating. Oddly, the single best tool I have found for rehab is a run of the mill compound bow. I have done the work after each injury to maintain shoulder mobility and prevent adhesions so in my case building muscle to protect the shoulder was most important to me. I picked up a Mission Craze bow for cheap and cranked it down to 15-20 lbs and just started shooting. It built muscle where it needed to be. My right shoulder now is good. I am as happy with it as I would be with what I would consider a very successful surgical repair. The left shoulder has been damaged less, but it has not progressed as well because I shoot right handed. It is far better than it was though. When I first started shooting it had a tendency to pop out on me and would fling the shot some feet off target. Now it's stable and I can shoot respectable targets to the point that my current bow, a No-Cam, needs to be balanced with a decent sight to keep up with how accurately I can shoot. Those of you who shoot target archery know That a hinge release is absolutely dependent upon stability and strength in your shoulders. Even when I haven't shot for months, that hinge is still my favorite release now. For my money, the best rehab of anything I went through was the Craze. As long as you start at very low poundage (which not all bows will adjust down to) and go very slow it can work quite well. When I considered the Craze initially it seemed a no-brainer to me. I couldn't even get another referral to an orthopedic for what I got the bow for.
Full disclosure: I do shoot all of my deer lately with a crossbow, but for other specific reasons
