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First off you should add some sort of counter magic, in this case either Dissipate or Rewind.

I would also consider adding Unsummon, this serves 2 purposes, #1 take out pesky creatures your opponents control #2 save your creatures from removal.

Finally I'd add fog, nothing buys you another turn like fog

Finally your deck is really good at stalling but you could easilly get overwhelmed by tokens or trample, I'd advise adding either Jace's Phantasm or Deadly Recluse at least in sideboard, I know that you're going for the defender theme but you need to be able to kill opponent's creatures sometimes

I get that you want to be sure to hit a Sands of Delirium but as it's an X cost activated artifact, having more than one at any given point in time is redundant (much like having 4x of a legendary creature).  I would suggest dropping down to 2x there and use those 2 spots to bring Tree of Redemption from your sideboard onto your mainboard.  Not only does it fit the defender scheme, but it ensures that you can survive even if they get past your blockers.

I agree with imsully about getting overrun rather easily, to which point I would almost suggest splashing white for a few cards.  Axebane Guardian lets you produce any color of mana and you could easily add one or two plains for the Gatecreeper Vines to go grab them.  Then, with a splash of white you open the door to Oblivion Ring and Detention Sphere for spot removal; Azorius Charm for an even more powerful Unsummon (it doesn't just return the creature to their hand, it puts it on their deck to screw up their next card draw too!); and Rest in Peace which lets you drop Tormod's Crypt from the sideboard and otherwise simply screws your opponents over (scavenge, undying, flashback, etc - GONE!).