Wood Spikes are traps used to defend structures by impaling zombies, players or animals. It's best to put wood spikes outside the fort, right next to the walls.  To make a Wood Spike, you need 9 Sharpened Sticks. Click Wood Spikes on the craft list to acquire the highlighted pattern. Place 1 Sharpened Sticks on each box to craft. Use about 3 layers of Spikes, or more, to make sure that no zombie can survive before they can reach your fort walls. The Trunk Tip is the best trap structure in the game; they make fine traps compared to wood spikes due to the fact that they don't break. However, they do give less damage and require a 2-block deep hole to place them in.  To make a Trunk Tip, you need 4 Wood Blocks; any kind of wood block will do (i.e. Birch Wood, Pine Wood, Burnt Wood or Wood). Press I; click the name Trunk Tip in the craft list to activate the highlighted pattern. In each box, you put 1 Wood to complete the crafting. Before placing Trunk Tip next to your walls, make sure to dig 2-blocks deep off the ground since this kind of trap is taller, which count as though zombies are standing one block higher. A Barbed Fence Wire is a craftable item but can also be scavenged around the world. This is commonly used to fortify a perimeter or to block breaches in walls during the night.  To make a Barbed Fence Wire, you need 2 Sticks and 1 Barbed Wire. Barbed wire can be obtained by crafting 3 Forging Iron; as a result, it will give you 15 barbed wires. Open your craft window. Make sure you have the requirements inside your inventory. Click the Barbed Fence Wire name to activate the pattern. In the middle, put 1 barbed wire then put 1 stick on either side of it. Make sure you have completely locked down the place. Block up any entry; place torches around your fortress, and then grab any range weapon you have. Zombies die because of the traps you set up earlier. There's no need for you to use your gun. Save your ammunition as much as you can and only use your range weapon for emergencies.

Summary:
Make Wood Spikes. Make Trunk Tips. Make Barbed Fence Wire. Keep Watch.