I have a LaTeX question for your amusement.

In maths mode, I want to have a symbol with two hats over it. I have obviously tried using (e.g.)
$\hat{\hat{U}}$
but this looks rather ugly: the vertical separation between the two hats is too wide 
Any clever idea on the topic? I am a bit desperate because I tried everything I could think of...
Any help is greatly appreciated,
Cheers
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For your information: I am using the document class "elsarticle.cls" and I have a fairly recent version of TeXLive (running on Mac OS X 10.5.8).