Defensive Demoman:

1. Pipe bomb traps
Be sure to lay pipebomb traps. You can use up to 7 pipes. Note:Those pipes are for your whole team, so multiple demos don't always work.
Some spots to lay pipes in: (in 2fort5)
1) Bottom of spirals or in the spirals
2) Flag hallways
3) Bottom of elevator

There isn't really much I can write here that isn't covered elsewhere. But there is more in the clan match defensive demo section.