I would suggest going over to the arrow spammers and pk them until they've had enough and leave. It's not really free kills if people are letting themselves get spammed by arrows. The arrow spammers aren't invincible. Are they annoying? Yes. You just need to shove them away. However, if it becomes trouble some as to where no one can even get into the top of the tower they should make the walls deflect the arrows like you mentioned.