I know that hostiles supposedly are clairvoyant and can sense whether or not they can reach their targets. They will not enter a tunnel that clearly serves as the entrance to fort if there's a locked door/grate/floodgate between them and your dwarves.
I've read about the possibility of using tame animals as bait, so I chained a couple of war dogs which I would keep accessible while having the path to my fort proper blocked. It didn't work. The goblins completely ignored my dogs, milling around somewhere above ground instead. When I opened the grates separating them from my dwarves they instantly started marching (or rather strolling at their usual leisurely pace).
Has this trick been nerfed or am I doing something wrong? I'm absolutely positive that my dogs were reachable; as proof, I've attached a screenshot.
The horizontal and vertical rows of engraved tiles below the chained dogs are where I put floodgates. The horizontal ones I kept open, obviously, to provide access to the bait; whenever I closed the vertical floodgates, the goblins would stop dead in their tracks, completely ignoring the bait.
Another thing:
I'm using a shaft-based layout of (mostly) 9x9 rooms with "lifts" in their corners. Cf.:
Will I gain something if I dig extra tunnels between the rooms? I was thinking about knocking out the center tile of each 9-tile wide wall. This has the potential for easier access between the rooms, but I'm a little hazy about how pathfinding in this game works. For a human, more/easier access would be good; but if I made my layout more complicated and gave my dwarves more pathing choices, would this have the potential of being more taxing for the pathing algorithms, and hence cause more lag?