unbreakable blocks

So im trying to make an anti-grief kinda datapack
what im trying to achieve here is that if you break a block in a certain place, it gets replaced and it wont drop an item
I cant use /fill repeatedly because it should copy the enviroment around it (its an armor stand that when you place down protects blocks in a certain radius)
and also i cant just put people into adventure mode around it because they should be able to do other stuff there (ex .fight mobs)'
so..???