How did you get the cliff that sheer (even before you cut into it)?
Umm.... put waste disposal stuff dumping water and -pig tail sock-'s out on to invading armies.
Find out exactly how far you can fling a noble/kitten/gobbo/etc. off the top.
White-water rafting for unlikable nobles only.
I used this world gen script, which another user posted here (minus the seeds):
http://www.bay12games.com/forum/index.php?topic=28325.0[WORLD_GEN]
[TITLE:SHEER CLIFFS SMALLER]
[SEED:2882067521]
[HISTORY_SEED:2195186091]
[NAME_SEED:4207536239]
[DIM:33:33]
[END_YEAR:1050]
[BEAST_END_YEAR:50:80]
[REVEAL_ALL_HISTORY:1]
[CULL_HISTORICAL_FIGURES:0]
[ELEVATION:1:400:1600:1600]
[RAINFALL:0:100:51:51]
[TEMPERATURE:25:75:51:51]
[DRAINAGE:0:100:51:51]
[VOLCANISM:0:100:1600:1600]
[SAVAGERY:0:100:51:51]
[ELEVATION_FREQUENCY:1:1:1:1:1:1]
[RAIN_FREQUENCY:1:1:1:1:1:1]
[DRAINAGE_FREQUENCY:1:1:1:1:1:1]
[TEMPERATURE_FREQUENCY:1:1:1:1:1:1]
[SAVAGERY_FREQUENCY:1:1:1:1:1:1]
[VOLCANISM_FREQUENCY:1:1:1:1:1:1]
[GOOD_SQ_COUNTS:1:16:32]
[EVIL_SQ_COUNTS:1:16:32]
[PEAK_NUMBER_MIN:3]
[OCEAN_EDGE_MIN:1]
[VOLCANO_MIN:6]
[REGION_COUNTS:SWAMP:0:0:0]
[REGION_COUNTS:DESERT:0:0:0]
[REGION_COUNTS:FOREST:0:0:0]
[REGION_COUNTS:MOUNTAINS:0:0:0]
[REGION_COUNTS:OCEAN:0:0:0]
[REGION_COUNTS:GLACIER:0:0:0]
[REGION_COUNTS:TUNDRA:0:0:0]
[REGION_COUNTS:GRASSLAND:0:0:0]
[REGION_COUNTS:HILLS:0:0:0]
[EROSION_CYCLE_COUNT:50]
[RIVER_MINS:6:6]
[PERIODICALLY_ERODE_EXTREMES:0]
[OROGRAPHIC_PRECIPITATION:1]
[SUBREGION_MAX:5000]
[CAVE_MIN_SIZE:5]
[CAVE_MAX_SIZE:25]
[MOUNTAIN_CAVE_MIN:1]
[NON_MOUNTAIN_CAVE_MIN:3]
[ALL_CAVES_VISIBLE:0]
[SHOW_EMBARK_RIVER:2]
[SHOW_EMBARK_POOL:2]
[SHOW_EMBARK_M_POOL:2]
[SHOW_EMBARK_M_PIPE:2]
[SHOW_EMBARK_CHASM:2]
[SHOW_EMBARK_PIT:2]
[SHOW_EMBARK_OTHER:2]
[SHOW_EMBARK_TUNNEL:2]
[TOTAL_CIV_NUMBER:15]
[TOTAL_CIV_POPULATION:20000]
[PLAYABLE_CIVILIZATION_REQUIRED:1]
[ELEVATION_RANGES:136:272:136]
[RAIN_RANGES:0:0:0]
[DRAINAGE_RANGES:0:0:0]
[SAVAGERY_RANGES:0:0:0]
[VOLCANISM_RANGES:0:0:0]
And then looked for an area with a magma pipe/underground river (the only source of water you are likely to find) and then looked to see how the elevation changed using the tab view. Example:
Then I would copy the save folder, embark and check out the site with 3dwarf to see if it was what I wanted. If not, back to genning. I must have gone through 30-40 worlds before I settled on the one above, and it's not really what I wanted.
As for your ideas:
A catapult (get it? cat - apult!) sounds like a great idea, I will do that.
I was already planning on using 'waste disposal' to dump magma onto the two towers you see on the ground, which would funnel it onto any attackers. (Invaders = off for now, though, along with everything else)
White water rafting: I will investigate this. It sounds awesome. I could create an artificial river flowing down the side of the cliff... mmm.
massive dwarf face is an idea as well, but my artistic talents are somewhat lacking. For that reason, I'm not even gonna attempt Mt. Dwarfmore.