In speaking of Peter's shield, I neglected to mention that Peter's shield comes up somewhere else: the single combat between Peter and Miraz. Before going into that story a quick introduction.
The shield that has an insignia. The insignia on the shield of Peter the High King over all kings of Narnia is the red lion. The red lion does not appear on Peter's sword, but on his shield. Now, of course, the shield has space for an insignia while the sword doesn't. But I find it interesting that the insignia is on the defensive tool, not the offensive one. Peter's defensive tool is marked by Aslan while his offensive tool is not. However, in the combat against Miraz, the shield becomes an offensive tool.
You'll remember that during the battle with Miraz Peter's shield goes limp - he cannot use his shield properly, he is open to attack. That is the view on the battlefield. But there's another perspective, not any less true: the red lion, Aslan, is lying limp no longer defending Peter. He has left him open, naked, and without protection. But there's a backstory, why is Peter's shield limp? Peter explains to Edmund and Dr. Conelius - the rim of his shield drove into his wrist causing (at least) a pretty severe sprain. In ther words, Peter's shield has been the cause of its going limp. Or, from our alternate perspective, Aslan has not merely left Peter open to harm, he has turned against him. Aslan caused the harm that left Peter without protection.
Aslan went from defending Peter to attacking him.
This is quite the lesson for Peter. But what has Peter done wrong? I think the answer is pretty clear. For most of 'Prince Caspian' Peter has been attempting to lead on his own, rather than paying heed to Aslan. He has, perhaps, quite forgotten that Alsan is the King and it is not Peter who will bring victory through single combat, but Aslan who may decide to use Peter's hand to achieve that victory.
Nevertheless, Peter has a solution - to have wrist tied very tight. In other words to limit its utility, make it unable to bend or rotate. Disable himself to rely on Aslan.
