Details questions

Using the built in world editor, i was today about to add some difs to test them out. Since the difs belonged to a kind of urban environment, i thought that i had to add some new textures also. This was when i ran into my problem: u only get to set one detail texture for each terrain block. I tried creating a new terrian block with another detail texture, but the only thing that happend was that they sort of interlaped each other, and no matter how i changed their position, it seemed that botch terrain blocks covered exactly the whole mission area. What should i do? Should i keep the urban area in a seperate mission, use another more general detail texture or is there some uggly hack solution to this problem?

In retrospect, i would like to express my apologies for the horrible english, it was late at the time it was being written, but i sure as hell wont edit it into something readable =)