the only issue that I can see here is the tree wielding troll. his attacks will go thru the wall so you need to build back from the wall or add a shallow ditch outside the wall to cover the distance. ive also used a ring of planted trees. the trolls will knock down the trees, yes, but i found that they cant walk over stumps and they actually hurt themselves trying to walk over felled trees. pretty funny watching a troll get stun locked on logs