How can I determine places where enemies might spawn during the night?

I barricaded all the entrances in a house at the farm for a night and I thought I'm safe, but zombie dog respawned somewhere, probably in the house or jumped through a window. So before I plan anything more I would like to ask about how to avoid such nasty situations.

How can I determine places where enemies might spawn during the night?

Solution 1:

As I understand it, there are two rules governing the spawning of zombies:

• Zombies will only spawn in locations that are dark
• Zombies will not spawn within a certain radius of a sleeping bag or bed that is owned by a player.

Therefore if you keep your stronghold well-lit you will be free from zombies spawning inside.

Other things to note:

• Crawler zombies can get through one-block gaps, even if they are 1 block above ground level.
• Dogs can get through one block gaps but only at ground level.
• Zombies can bash through unexpected places like if you have a large mine attached to your base, they might be able to break in via a weakness near the surface.
• Zombies can spawn on the roof of your house sometimes depending on where your sleeping bag is. This can let them get in if you have a hole or hatch on your roof. This is especially likely when you trigger a spider zombie scout party (when you see 3 spider zombies lurking fairly close together, shooting one will trigger a horde to spawn).