Holy Walll

I love funky themed decks! :) And this is probably not a very serious deck but I have some suggestions if that's ok.

If you want to keep it Mono-White here are some cards for a win condition beside relying on Serra Ascendant: Wakestone Gargoyle [lets you swing with Defenders], Sunweb [a big ass flying defender for 4 I think], Honor of the Pure and Crusade [buff your board for when you do swing]. And come to think of it: Archangel of Thune would be absurd here [when you gain life put a +1/+1 counter on each creature you control].

If you splash in Blue, then you can add Doorkeeper [mill opponent based on defenders], and throw in Wall of Air, Plumeveil, Wall of Denial, and Sanctum Plowbeast [has plains and island cycling to help with lands]. Maybe even toss in an Alluring Siren to guarantee they swing with something each turn to keep your life gain up.

If you splash in Red, then tossing in Vent Sentinel gives you some massive damage based on defenders, and you can get some cool defenders like Aether Membrane, Flamewright [makes tokens with defender which you can sac to ping] and red has tons of cards that guarantee you get attacked to maintain your life gain but Basandra, Battle Seraph [kick ass angel with {R} target creature attacks] and Goblin Diplomats [probably the most efficient way to make everything attack] are my two personal favorites. But if you are dead set against creatures without defender then there are plenty of red spells that can do it too!

If you splash in Green, then you get access to the awesome Treefolk shit and then throw in Assault Formation for 2 and your defenders can now assign damage based on their toughness not power. I'll let your imagination run rampant on that one. There are gobs of Treefolk tribal stuff that builds off defender and removes defender and things like that.

Splashing in Black might not get you much at first glance but it'd be evil. You could get things like Souls of the Faultless [like Wall of Hope but they lose life as well as you gaining it] and you'd get things like Wall of Souls [when dealt damage opponent takes damage], Wall of Bone [regenerates for one], Tree of Perdition [swap opponents life total with its toughness], and Wall of Limbs would sync well with your life gaining [when you gain life put a +1/+1 counter on it, then pay like 7 and sac it: deal damage to target player for each counter on Wall of Limbs].

Just some quick thoughts based on my own attempts to do a Green/Black treefolk deck for a friend, a blue defender deck for me once, and a couple quick searches.

Good luck and have fun with your deck!

Your deck name is holy wall, but I see you have a very unholy wall in there, assuming you don't subscribe to the Machine Orthodoxy's tenets. Cathedral Membrane is Phyrexian, and Phyrexia is considered among the least holy in the multiverse, just FYI.

One thing to consider is that you don't have any way to deal with flying creatures. Maybe look at swapping in some flying defenders like
Wall of Reverence (also helps you with life gain if you can get something with any power onto the field) or the aforementioned Wakestone Gargoyle. Also look at Angelic Wall (fairly plain but low cmc) and also Wall of Swords.

Cheers!