Aegis Arcanum

You create a powerfull shielding barrier arround a willing creature you touch, this barrier is concentrated on a silvered necklace worn by your target. While you are concentrating on this spell, the target gains a bonus to AC equal to your spellcasting modifier. Should the target suffer any damage, it can use it's reaction to reduce this damage to 0, hereby destroying the silvered necklace and ending the spel.

Should the spell be ended by an effect such as dispell magic or simular effects, the necklace is destroyed.