Undergravel filter with sand???

[zima]

Does anyone have any experience with u/g filters? I am hearing really mixed messages about them, ranging from "very useful" to "very dangerous" due to bacteria accumulating beneath it. I am using sand in this tank, and needless to say, the sand will pretty much cover the whole bottom, thus, it would seem, defeating the purpose of the u/g filter. Any ideas/suggestions?

hanx