Originally posted by Dwarflord:

A Ballista can't even hit the only things I need them to hit...fliers. Best defense against everything else is location...a raised island lined with player base items.

That's one I didn't think-of, though I've noticed they don't hit me when I'm in motion. (So, if you need to work in front of free-firing ballistae, just don't stand still? Should work, mostly)

Wouldn't you also like them to hit the seeker soldiers? The fliers aren't as dangerous, it seems to me. A tactic I want to try is to get a seeker soldier facing me with its rear toward a ballista. Of course, if the bolt misses, the player is also in the line of fire. But that's my idea of fun.