Thanks a lot for the suggestions.
First of all, you are right. I have a tendency to "EDH" my decks, though the main cards are 3s or 4s:
4
Perimeter Captain3
Wall of Tanglecord3
Angelic Wall4
Overgrown Battlementand of course
4
Assault FormationRegarding your suggestions, I already have 2
Stalwart Shield Bearers.
Order of the Stars is too weak to attack later and
Wall of Shards too costly.
Regarding
Wall of Swords &
Wakestone Gargoyle, I wanted to keep defenders under 3 power, so they won't be hit by
Dusk // Dawn. The idea is to hit with toughness, not power. This also renders
Wakestone Gargoyle ability almost useless.
Wall of Omens would be great, probably substituting the Perimeter Captains, but in my group play we have a rule to enhance homebrewing - only cards less than a certain price are allowed (2 euro, around $2,5 - shop prices). It limits your options, but encourages you to find alternatives. That's why the deck is so cheap.
And this rules out
Wall of Omens, all your planeswalkers suggestions, and
Shalai, Voice of Plenty.
And also a great card for a GWB version of the deck:
Doran, the Siege Tower. It could be great with
Treefolk Harbinger as tutor (but then, you would need a non-defender, high-toughness version of the cards):
Nyx-Fleece RamLingering Souls +
Tower DefenseIn fact, if you are thinking about an EDH version, it should definitely be your commander.
Thanks for the feedback !