No - it's not me telling off a teenage son or daughter.
I've been thinking about what that Liche-Lord might do to combat an army coming to to kick his butt - an army with wizards as well as warriors. Of course, he could just Blow Me To out of there but he would lose all his treasures...
...so what he needs is a Not In My House Spell! It stops beings entering. Simple. And, being cunning and malicious, he drops it long enough to lure some inside and then slams up the barriers.
He can see the army coming in his scrying stone and now the trap is baited.