I don't know how these tower spamming rook players do it, because when I try to, 75% of the time, if not more, I get a red fading text saying "aborted" when I try to place the tower.
My guess is that this is down to a very picky collision detection, but it wastes so much time that I am filing this as a technical issue, because surely the game could move the tower an inch or two to a space that's free instead of cancelling the action?