[Modern] Defender Milling Deck

Okay, first off, just to be sure, you're aiming for a Modern deck, right?  The reason I ask is because shy of Harrow the deck is nothing but standard cards.

That being said, modern offers a LOT more options for milling the opponent successfully than we have in standard.

First off, drop 1x Duskmantle Guildmage, all the Jace's Phantasms, and Mirko Vosk.  If you're going for defender mill, either go big or go home.  I would also likely drop the Doorkeepers too as you'll be much better suited to rip into your X cost mill effects than simply tapping Doorkeeper to mill 3-4 cards.

So what do you add?  Overgrown Battlement is a NICE replacement for Doorkeeper in that it offers you essentially Axebane Guardians 5-8.  Why not toss in some Clones and Progenitor Mimic?  Then you're talking Axebanes 9-14 (with two Mimics) while also offering you some added defensive flexibility.  They play something huge?  Then you get one and can continue to stall the board.

A few other cards to consider:

Hedron Crab - not fitting the defender mix, but an 0/2 that will mill every time you drop a land?  That has some HILARIOUS potential.  Even something like Ghostly Flicker can now be mill six.  If you have more than one crab out, well, you get the idea.

Keening Stone - this card doesn't get much love because of the costs behind it, but read that text, you mill them equal to the total number of cards in their graveyard.  As such, if you can get HALF of their deck in the yard, you will win with ONE trigger.  Don't forget it's not exactly like you're going to be short on mana with all the Axebane Guardians and Overgrown Battlements.

Breaking // Entering - it's not quite Glimpse power, but it comes with an added bonus.  Again, as you're not struggling with the mana and axebane can provide red and black to cast, this lets you mill them eight and then pick their best creature to sit on your side delaying the game.

Thought Scour and Pilfered Plans - good options to help improve consistency via card draw while still not straying away from the mill strategy.

Reap Intellect - I sound like I'm beating a dead horse here, but with a TON of mana care of the axebanes, you could cast this rather hilariously exiling EVERY nonland card in their hand and all the copies of those throughout the deck.

Now onto MUST haves.  You NEED ways to stall the game.  Here are a few options:

Fog, Moonmist, Druid's Deliverance, Hindervines (in a pinch). Unsummon, Silent Departure, and Cyclonic Rift. To name just a few.

You also NEED removal.  Regardless of what happens with regard to life totals.

Devour Flesh, Tribute to Hunger, Ultimate Price, Murder, Grisly Spectacle, etc. etc.

Remember that milling decks typically aren't the most successful, as you've made your job a full three-times harder before the game even starts by adopting that path.  But some of these suggestions should provide some added milling power.