As usual, some human merchants turned up to trade me their goods. This is a good sign, because I have heaps I want to get rid of. Then, all of a sudden, the next thing I know, a vile force of darkness has arrived.
"All good, my burrow is set up properly, so I can call everyone back inside". So I check out the size of the siege, see what I'm up against, and call all my workers back inside. By the time I've tried to convince my dwarves that being on break did not give them leave of my burrow restrictions, I had completely forgotten about that caravan that turned up.
It also happened that the goblins appeared where I had some of those annoying "traders" that just sit at the edge of the map doing nothing. So, while the goblins are distracted killing off those useless guys, all my men come inside. I was about to pull the lever to close off my drawbridge, when I noticed that a human swordsman had just killed 2 of the goblins single handedly, and decided I'd let them come in.
So, fortress shut, traders and all dwarves inside, and goblins preoccupied with traders. So far so good.
Out of the blue, along comes a weregiraffe, right in the middle of the hoarde, and then decides to start killing the goblins for me, before turning into a human and killing another. Now, I've just let my gates open for them to come flying into my cage traps and give my archers a little target practice.
Quickest and easiest siege I have ever encountered. Not a single injury to my side