I am creating a flat desert map. how do I create ongoing scenery outside of the sky box?(like the continuing water in Death island)

Make it go very far, so you can't tell that it really ends. Also, use a invisible wall so people can't go far enough to see.

How do you create an invisible wall?

Just have the faces where you want the wall to be, and give those faces the "+sky" material.

WRONG! Make the faces and give them a +unused* material.

Either way works, actually. I've used +sky, and it doesn't seem to harm it any...

But, yeah; I forgot about that one. Thanks for mentioning it.

If you use a +sky, the level ends right there and you can walk over to it and see where the water plane stops. You would need the +sky very far back. And have a invisible wall stopping you from getting anywhere near to the edge of the map.

I think that the +unused * would be best, but I swear I've been able to put scenery outside of the map past the skybox geometry in sapien. Actual playerclipping is best because that's what it's made for; preventing you from getting places.

You can't put scenery outside the BSP. Even if you did it would not show up in-game.