Got this from Alex, a suggested contact further up in the thread. Interesting info, especially on the stretching side of things. Hmmmm.
I use a theraband to warm up just before getting on the river as suggested by my PT. Basically the theraband is placed around a stationary object (roof rack, tree, large dog) and I do some forward and reverse stroke motions (20-30 reps each), also do external, internal rotations, and circular motions. Not a lot of force is placed on the band so as not to strain anything. You can do any variety of warm ups with the theraband that suit you. Any stretchy tube or band will do. The routine should last 5-10 minutes so as to get the rotator cuff muscles warmed up and ready to go.
I was discouraged from stretching the shoulders prior to putting on, If I understand correctly, the shoulders are flexible enough as is, they just need to be warmed up. The exercises done in the gym or at PT stretch out the shoulders enough. I made the mistake of extensively stretching my shoulders, thus the poor prognosis i suffered.
I do stretch my hamstrings before putting on, my back is in poor shape but the stretch helps that alot.
Routine shoulder excercise is key, otherwise the warmups wont do much good. External and internal rotations, also google "side lying abduction" or ask a PT about that one, that has seemed to be the final excercise that made my bum shoulder feel bomber, post surgery. All rotator cuff excercises are with slow reps with light weights. I do a 6-10 minute warm up on a rowing machine before hitting the weights, same idea as using a theraband before the river.
Avoid bench press with a bar, military with a bar, behind the head pull downs and pulling up a bar from the floor (cant remember what that last excercise is called). A PT should be able to guide you away from the exercises that do more harm than good.
Probably more info than you wanted, but that is what I know so far, in a nutshell. Hope it helps and good luck.