I know it sounds kinda OP, but for those of us that would like just a little security without always repairing and upgrading.
You might be able to get close to what you want with existing configuration options...
You can change the size of the protected area provided by a Land Claim block.
You can configure the game to allow you to have more than one Land Claim block.
You can configure the area protected by a bedroll.
You can configure the amount of damage the AI can do to blocks.
Set the Land Claim Size to something large. I've no idea what the maximum allowed would be. If you set it via the "New Game" window, 71 is the largest preset they've given. If there is a max and its not big enough, let yourself place more than one Land Claim Block.
If its bedrolls that suppress spawning, then you can change that radius too.
Then, build walls around your perimeter to keep out the random spawns. Then you can have some fun of managing the maintenance of your walls. If you find the Z's are doing too much damage to your walls for your tastes/goals, you can change the BlockDamageAI setting so that Z's do less damage to blocks.
serverconfig.xml
<!-- Land claim options -->
<property name="LandClaimCount" value="1"/>
<!-- Maximum allowed land claims per player. -->
<property name="LandClaimSize" value="41"/>
<!-- Size in blocks that is protected by a keystone -->
<property name="LandClaimDeadZone" value="30"/>
<!-- Keystones must be this many blocks apart (unless you are friends with the other player) -->
serverconfig.xml
<property name="BedrollDeadZoneSize" value="15"/>
<!-- Size (box "radius", so a box with 2 times the given value for each side's length) of bedroll deadzone, no zombies will spawn inside this area, and any cleared sleeper volumes that touch a bedroll deadzone will not spawn after they've been cleared. -->
serverconfig.xml
Code:
<property name="BlockDamageAI" value="100"/>
<!-- How much damage do AIs to blocks (percentage in whole numbers) -->