Walk him in hand around the field. Let him stand and watch the deer. When he's near them, let him graze some. Grazing releases endorphins, helping him to relax and feel positive.
Also, try putting some Vick's on his nose. This will help block the smell of the deer, which should help calm him some. Once he's used to the sight of them, stop using the Vick's and let him get used to the smell of them.
As for his reining, try an indirect rein, kind of like a neck rein and direct rein at the same time. Pull your turning hand out just a little and back just a little. Pull your off side hand in toward his neck, but not back. Look in the direction you want to go, shoulder's back. Step your foot into the stirrup and away from the horse a little on your turning side. Put your leg against him on your off side. Does that make sense?
Have you tried neck reining him?
If all else fails, start on the ground from step one, like he's a totally untrained horse. Work on giving to bit pressure, slowing working toward ground driving.