It is really next to impossible to truly isolate a muscle even doing "isolations" let alone when doing compound movements. Like ENNORIS said coupound movements result in growth. Unless this is to become the "how to screw up your shoudlers" thread, you'd be better off maintaining proper technique and concentrating on getting progressively stronger at the primary movements. I just said recently what I think is a good way of putting it: Instead of using the movements to make your body better; make your body better at the movements. Growth is a happy side effect of that.

I think most of the effort should be for that. If you weigh, for instance 185 and you get your military press up to 150, 160, 170 or beyond then you will have some big shoulders. And big everthing else. Providing that pressing is a healthy activity for your in the first place and you have not impingements, etc. that prevent it.

If you want to isolate the shoulders further beyond that then use isolations :). It is much safer to do some laterals and such then it is to modify a heavy pressing movement to put your shoulders in a vulnerable position.

behind the neck will weakin your rotater-cup alot of training books out now will tell u that