In Goblin Camp, can doors be locked at all? Some Minotaurs just seemed to take the first door to my camp without any hesitance. Might this be by design or can I actually seal my camp using doors?
Nope, anything with hands can open doors, which is why you need to station your military orcs near your entrances, also since they added flying creatures, you can't be 100% safe since bees will just fly over your walls.
You're best defence is to pause the game when you see the monsters coming, and reposition your orcs so they can deal with the threat. As long as they're well equipped you'll be fine.