Dungeon Making Woes

[John Joe Johnso]

Hi all, I'm DMing for my group of friends and I've run into a problem.

First off, I decided to build a dungeon that is more or less a maze loaded with booby traps, riddles, puzzles, monsters, etc... now that I think about it, that sounds like any typical dungeon. Anywho, one of my friends is a level 11 spirit shaman and he can turn incorporeal (spirit form) once per day for 1 minute. How do I prevent him from completely bypassing the maze, scouting ahead, and reporting back saying to the party "yeah I found the bad guy?"

The monster manual says, "An incorporeal creature can enter or pass through solid objects, but must remain adjacent to the object’s exterior, and so cannot
pass entirely through an object whose space is larger than its own." So... very thick walls/doors = impassable wall?

[Azoth]

Thick walls, mechanisms that change the layout of the maze every (insert time frame here), setting it to feel too dangerous to risk seperation, making the maze large enough that he can't scout the entire thing in 60 seconds, there are a few items scattered throughout books that can make walls impassible to incorporeal...kind of like a Ghost Touch White Wash of sorts.

[Pilo]

Antimagic field will prevent him to use his power.
However, there are other ways:
You can add some magical portal to link some parts of the dungeon.
While incorporeal, he will still be visible.
Finding where the bad guy is is not the same as finding a way for everyone to go there (if teleportation is prevented by a way to block teleportation)
1 minute is only 300 feet of movement.

[Kane0]

Make sure you dont stop him using it completely Though. Make a couple cases where it can be used, but not to bypass large parts of the dungeon. That way he feels like he has used his resource to his advantage and you have an intact dungeon.

[NevinPL]

Make sure you dont stop him using it completely Though.
This.

As for your question, Stronghold Builder's Guidebook (3E) has something that may interest you - Ethereal solid (wall augmentation that blocks ethereal intrusion) for 12k gp. I also remember something about some paint, or something, that would do something like that, but I can't find it now. Found it - Ghostwall Shellac from Dungeonscape. But it lasts only for 4d6 hours.
You can look here for some other ideas:
http://www.giantitp.com/forums/showthread.php?t=101473