How to make blocks in spawn unbreakable in survival?

So on my multiplayer server on Minecraft Education Edition I can't seem to figure out how to make the blocks in spawn unbreakable. I know adventure mode fixes that but it's a survival world. I don't want them in adventure, so how do I make the blocks in spawn unbreakable?

There are a few methods in doing this

1. Unbreakable blocks

A list of unbreakible blocks in survival include bedrock, barrier blocks and command blocks

2. /clone command

Using a command block clone a duplicate of your spawn with a repeating command block

NOTE: making edits to your spawn is only possible it the duplicate being cloned

3. Cobblestone generators

Using multiple cobblestone generators and pistons to replace fallen walls

4. Barrier blocks

Place a beautiful background and coat the inside with barrier blocks

NOTE: to get command blocks and barriers can be done in chat with “/give (name) command_block OR barrier