These are some good ideas. I may borrow a few of them myself. I currently do alternating rows of stone-fall and cage traps to stop essentially anything that tries to get inside my fort. That's what stopped the Necromancer and Goblin sieges that attacked me at the same time. (Im trying to figure out how to get my dwarves to just toss 2 of the necros down my nigh bottomless pit, but they wont do it. Suggestions?)
Stone traps are pretty fun, aside from the mess. Cage traps aren't my favorite though... I don't have fun with the attackers when they wander into my cages. I like sending my military out to chop up the enemy gobos.
my suggestion is using a minecart to launch them, whilst still in their cage down there. If you "fire" the cage out (so aim a minecart which has speed at a wall with a space above where the minecart hits, minecart slams into it and contents (i.e cage) fly out, contents fly out of cage because that is what happens, cage + necromancer fly down bottomless pit.
| PIT W C_____________
x = floor, X = ceiling | = wall, W = wall which minecart hits, C = minecart, _ = track where minecart has come from. Obviously for the cage to go through, there is empty space.
Not great with drawings, hope that's enough though.
My guess to why cage traps were unsuccessful is simply not having enough, i had literally 5 mechanics out of 60 dwarves, and another 5 of them were generally replacing traps for 90% of their lives.
In a save which has repelled 4 simultaeneous ambushes (~4 goblins in each) i had 20 cage traps on each side as close to the edge as possible, with 4 gaps inbetween (on a smaller map than a standard embark) 8 of the goblins were caught in said traps, an additional 4 thieves/snatchers of 5 were caught. 4 goblins fled after crossbowmen took out 1, legendary hammerdwarves finished up.
On a different save, i had closer to 300 cage traps, i actually managed to capture 100% of some ambushes, which is pretty impressive i think
Bear in mind i am still fairly new, i have yet to work out a lot of stuff, for example today I used my first screw pump, and was definitely impressed, was expecting like 1/7 of water each second, heck that guess was wrong
(more like 3 full 7/7 tiles) and surprisingly easy to use.
Remember, do what's fun for you, ambushes are really funny, so bring em on, let em come and mash em up, invent some defenses, going to try flooding them out soon, using my new knowledge of screw presses
(make a water tank, filled with ~200 7/7 waters, open 4 floodgates as goblins approach entrance, amusement ensues).