Here is a great rear deltoid exercise that some will find a little too embarrassing to do. It really works the back shoulders very effectively. It’s much easier to control form for this exercise while using the upright bench. Have the weights meet up under the bench at the starting point of the exercise.
Rest forehead on comfortable, not quite waist-high bench. Hold dumbbells, arms straight down, elbows locked. Raise dumbbells out to shoulder height, even with ears. Hold position momentarily, contract rear deltoids (do not swing dumbbells). Finally slowly lower them to starting position. Do 12 reps, then rest 7 seconds, then do 8 reps, rest the same time and then do 6 reps, rest and finally do 4 reps.