Modding Help Force Tile Protection on Microdungeon

I'm trying to get my head around dungeons, but have gotten stuck on tile protection. I've set protected to true within the metadata, and found my dungeon 'in the wild' (as opposed to using /placedungeon) but I could still dig straight through them. I'm wondering if I can use object properties within Tiled to set specific parts of a dungeon as protected, and if so what is the proper syntax to use? Also open to other suggestions as to why protection doesn't seem to be working if other people have solved the same problem, I may be doing something very obvious without realizing!

Code:

{
    "metadata" : {
        "name" : "tabularasamicrodungeons",
        "species" : "generic",
        "rules" : [],

        "anchor" : [ "ojprecursorship" ],

        "gravity" : 80,
        "maxRadius" : 1000000,
        "maxparts" : 1,
        "protected" : true
    },

    "parts" : [
        {
            "name" : "ojprecursorship",
            "rules" : [
                [ "maxSpawnCount" , [1] ]
            ],
            "def" : [ "tmx" , "ojprecursorship.json" ]
        }
    ]
}

​