1. Try get some successful action from an assassin. If you succeed, not only - supposedly - the character's rating will increase, but you should ASAP post the novelty, so that the whole community would rejoice at such a wonderful announcement.

I missed the movie for the only successful sabotage attempt in my English campaign only because I was soooo bored to see that assassin getting caught again and again.

2. In sieges or pre-battles, in deployment mode, you should have that option as special ability for longbowmen - hover your mouse over options, down-right corner, and you'll notice.