Damage fences

Electric fence

To make an electric fence, you use the regular recipe for a fence, but make it copper instead. You need Redstone to power it or lightning to strike the fence before it can shock a mob that runs into it. If you power it with Redstone it will destroy the Redstone power source after it shocks the mob.

Flame fence

To make an flame fence, it takes two steps. First you make a Netherrack fence by using the same recipe for any type of fence, but you substitute Netherrack. Next you use a flame charge with the Netherrack fence to make a flame fence, which burns a mob when it runs into the fence.

See Different Obsidian and Netherrack Blocks for how to make a Netherrack fence. https://feedback.minecraft.net/hc/en-us/community/posts/4409686291085-Different-Obsidian-and-Netherrack-Blocks