Hussar
Legend
He is an AMAZING DM!
I have become a better player because of his style....and yes I could have it made (I was not skilled enough of a character to do so)...it cost more then a normal shield and took time but it was worth that so I could have the shield...also gave me Resistance to Acid Damage if the Shield was being wielded. He argued that an Ankheg's shell would have this...so the shield should as well.
Hey, whatever floats your boat.
For me, and I suspect a number of other DM's here, this is a very douchey move by the DM and it's the sort of ridiculous pixel bitching stuff that gives DM's a very bad name. It's no different than the DM who has your character freeze to death because you didn't write down "winter clothes" on your character sheet.
When you run games yourself, do yourself a favor and don't treat this as a "teachable moment". Just remind the player, "Hey, are you going to put your holy symbol on that?" and move on. Aha gotcha moments are not, generally speaking, received well and outside of a very few, somewhat outspoken fans, it's almost universally condemned as poor DMing.