Shattered Kingdoms

When you cast gate in a no-gate room, you just get the "You failed" message. I didn't know it was a no-gate room until I lost all my mana save one gate spell and I walked one room southeast and casted the gate on the first try.

I was thinking something like "Anti-gate magic closes your portal" for a succeed in a no-gate room. "You failed" for the fail of course.

If you fail the casting of the gate spell, it will only cost half mana.

If you succeed at casting it, but the target it resistant, or dead, or the room is warded it will cost full mana. A message would be cool for something like this but you can also use deduction.

You only know that for sure if you're gating to portal stones though.

No gate rooms keep gank squads from gateing to people like priests and face rolling them in their temples.

No-gate rooms come in many different colors.

I agree that there should be something similar to the message no-recall rooms return when you cast 'Word of Recall'. Those say "You can't recall from here." You could do something simple like "Gates or rifts cannot be created here."