If anything attacks you, The attack takes no effect, The shield takes this damage. Its health is unlimited. But With every thing That makes contact with your shield You must roll a 1d6. and if you roll a nat 1. Your concentration wavers and it takes a considerable effort to keep the shield up. This effort is decided by the attacks damage, strength etc. The dm will decide. But if you succeed, You cannot be attacked or charmed. You can attack outside of your shield. but you roll depending on the spells level and strength, on a failed roll, You fail the spell. on a 1 to 3, your concentration wavers. see above.