The only good defense against werebeasts is not to be near where they are without a good wall in between (preferrably decked over to protect against climbing). However, if you would be prepared for the micro management, you could have your militia constantly reposted to be near the single outdoor worker, but that is likely to get some militia killed and others to get infected by lycanthropy. Another option would be to assign a pair of war trained dogs to each outdoor worker. An attack would likely result in a couple of dead dogs, but they might buy their charge the time needed to escape to safety.
A third option is hunting dogs postings dotting the map to detect werebeasts and draw their attacks. If you put them in 3*3 houses (i.e. single tile inside) with a door and the walls modified to fortifications, the werecreature would spend time destroying the door to get at the dog, you would then get additional time to get your dorfs into safety. If you're really lucky the morning would come before the door is completely destroyed.
Various traps relying on the weres being building destroyers can be used as well (e.g. were destroys door, which causes liquid [preferrably magma], to pour out to activate a pressure plate that destroys a support that causes a collapse on top of the were Should also work on titans/FBs. I've created such designs, but never seen whether they work since nothing has attacked them as yet. In principle, a juicy secondary target, such as a door in the liquid ought to increase the likelihood the vandal is still underneath when the collapse is triggered).
Naryar beat me to most of the above.