I hate that feeling in CMZ when I build an indestructible base and then when the zombies come out, they pose no threat to my survival. The game quickly gets boring as the zombies cannot reach you nor attack you, thus eliminating the challenge. I propose an idea that, if implemented in a future update, will make gameplay challenging and fun, whether it be early or late-game.
-Zombies spawn in greater numbers and further away (to give the rifle a purpose and to give a moment of "HERE THEY COME!")
-Metal plating (Craftable Item; comes in iron, copper, and steel [Requires 2 bars of the item it is made from])
-Steel bars (Alloy; requires 1 iron bar, 2 coal, and 1 copper bar)
-Sensor Array (Craftable Item; requires 2 copper and 1 sand)
-Autocannon (Autoturrent; made from 3 of any alloy [each alloy determining HP, copper-10 iron-25 steel-50] and a sensor array; uses normal ammo; is good as long as monsters dont hurt it [dragons and skeletons DESTROY turrents] and as long as it has ammo; medium fire rate)
-Dragons come more often
-Flak Cannons (Autoturrent; use grenades for ammo; same HP and crafting principle with the autocannon; only shoots at dragons, but will annihilate them; very slow fire rate)
-Landmines (Will detonate when anything steps on it, that includes players)
-Random Events (Giant Zombie horde; Wave of Dragons; plays a soundtrack to signify event)
-PMSGs (Player Mounted Shield Generators; special slot in inventory; different types of PMSGs, each with different stats [damage able to absorb; recharge rate; movement reduction)
-PVP option for servers
-When autosentries (autocannons and flak cannons) are destroyed, they explode, damaging blocks around them (equivalent to a C4 detonation)