Is it possible to simply lock a wooden door without mods?

If you have to use a mod, then forget it.
But is it possible to either make a wooden door act like an iron door, or just not be able to get through it anyway? I tried a repeating command block to clone a closed copy of the door, but it still opens for a split second and you might be able to get through it with speed potion or something which i dont want.
And no I don't wnat to actually use an iron door if I have to