I did most of this unit years ago (it's a long story). I don't recall how I did the shield on this one, but on newer units I've started cutting a piece out of the center of the shield and pasting it onto a feature on the unit itself to make sure the shield is in the same position relative to the unit on each frame.
For example, on my most recent spearman I cut a hole in the center of the shield. I then pasted the shield so that the hole was right over the unit's forearm. Then I pasted the part I cut out back over the hole.