SplashCanyon just experienced its first siege in 5+ years (only had one before, I guess climbing up the mountain is a less enticing prospect even for goblins).
I was thrilled, since it, finally, gave me a chance to test my tidal wave weapon!
End result: Big, big disappointment. The goblins took my intended path up the mountain, so far, so good. I waited for them to get into perfect position, and then I pulled the lever. And sure, they were drowning and all. Occasionally. I had discounted the fact that goblins, it seems, swim rather well, even when being drenched by three z-levels of 7/7-deep water. Just enough to get up to take a breath which allows them to stay alive, at least. The fact that they had slopes to stand on (I left them to be able to lure the goblins up the mountain) might have helped them some in this, not too sure how that affects things. Either way, I was half expecting the wave to swoop them down the mountain, which sadly didn't happen, it just seemed to knock them into stuff, stunning them. I clearly need to rethink this... There has to be a way to make it work (apart from substituting water with magma).
Something that did work well though was my line of weapon traps, originally intended on keeping snatchers out.
End kill score: Tidal Wave Weapon (which I spent 3+ years working on): 2, Weapon Traps (took me a season, at most): 6...
One honourable mention however is one of my inexperienced (proficient) swordsdwarves with only three goblin snatcher kills to his name before the siege.
After most of the goblins were dead, and the rest had retreated, they left a Voracious Cave Crawler milling around the mountain, seeming lost (he moved three tiles and then back again). So, I sent my squads out to kill him, telling them to gather at a safe distance.
One dwarf, however, thought it'd be a good idea to charge the enemy alone, with the rest of the squads far from in position. Great, he's dead (or so I thought). Sure enough, it started poorly with him trying to cut the crawler in the head, the blow doing no damage whatsoever, and in turn he got smacked into the mountain. But lo and behold, he managed to turn it around, and in the end he stood as victor, with NO damage done to him whatsoever (he only got stunned during the battle).