If you need to prevent players from destroying only specific parts of the world, but you don't want something like claims, something like this is probably what you need

Do /team join trusted to be able to use it (or /team join trusted [​username] to let other people use it)

You can give yourself the item that marks the protected area with /trigger giveprotect, then simply place the armor stands wherever you want

The armor stands/markers are invisible (if you are on spectator mode you will see them as semitransparent) and have no hitbox, so the only way to get rid of them is /kill

Each armor stand protects a spherical area 20 blocks in every direction

Every player in survival mode will be set to adventure mode when entering a protected area, and every player in adventure mode will be set to survival mode when leaving it. Other game modes are not affected.