It's so dreadful when you see an invading Troll take down an entire field of baby carrots you just planted. Once I get carrot production up and running, I'll stash 100 seeds in a box in my fortress, just in case they all get smashed I can start again faster. That said, when the invasion comes, make sure you kite those guys around and don't lose aggro, if you can. That's when the mobs start doin' real damage... when they can't find you (in their circle of doom)!