For the past several versions I have been experimenting with dwarves living humie-style. Personally, I like this style of play for the challenge and the aesthetic possibilities of a spread-out city. Whenever I start a traditional game, I get too caught-up on vertical fortress design and efficient stockpile/workshop layouts. The end result is a machine that is so efficient that I get 200 dwarves by year 4. Also, with the latest version that adds a lot of desirability to dwarves living and working on the surface, above-ground towns seem much more viable and immediately profitable. That's why I like above-ground dwarves.
I embark in a very flat, heavily-wooded area and proceed to make all my structures out of wood. Aside from my quarry, nothing can extend more than two layers underground. My more successful towns have had churches, several dining halls, and most industries with a relatively efficient work flow. However, all my towns have fallen to a single threat: gobbo ambushes.
The main problem lies in the fact that an open-air town is difficult to encircle with a wall. The amount of time and dwarfpower required to completely wall up a sizable town is considerable. I rarely manage to establish a secure perimeter, complete with patrolling soldiers before an ambush of goblin lashers massacre my dwarves.
Another problem is the miserably slow expansion rate. Dwarves construct things really slow and, especially with only your starting seven, you can't build any structure larger than 4x4 with a roof before your dwarves need a place to sleep. Besides that, the sheer amount of material you need to build a building adds loads to the overall construction time.
Anybody got any thoughts they'd like to share about above-ground towns? Any interesting layouts? What's a fast and easy way to secure a perimeter and keep your dwarves safe?