I had a thought about the MitD not being able to see the gate/rift that i wanted to share with this thread. it has been established that the snarl's prison doesn't work well with divine energy; that the stuff has been nullified there. We also know that the rifts are resistant to divine investigation. Even when the dark one looked at a rift directly all he learned was: its a rift, and there is something very powerful and hostile on the other side.
My idea was that something about the "anti-divide energy" aspect of the prison makes it so beings that use the same energy have trouble noticing/ perceiving it. If a god only notices it when his attention is directly drawn there, maybe something of a similar type but with less power can't see the rifts at all. Perhaps the MitD is something that uses divine energy, like outsider from alignment based plane, or something that is thought to have partially divine heritage. Another option is a creature who's natural abilities mimic divine magic, if it wields the same type of divine power maybe such a creature would be similarly blocked from seeing the rifts/gates.
So, what do you guys think?