Talk:Assembler/@comment-174.1.136.225-20111118211216/@comment-4583259-20111119082001

If you have a structure above-ground with a roof (a "house"), or if you are underground, you can keep Astronauts out by making the door or tunnel just two blocks high (big enough for you but not for the astronaut).

If it's a house above ground, and without a roof (like an open courtyard or a penned in area) astronauts can climb the wall and get over it unless it's 5 blocks high. Even then they can often get in or out by climbing an adjacent wall and jumping. See User_blog:Mrob27/Astronaut_Wrangling for details.

To keep other Mobs out, other types of walls or doors are needed. See Fences.