How to hide error messages automaticly in libnotify in gnome shell?

Im using ubuntu 11.10 and gnome-shell 3. I`m using Guard to notify test pass or failure.

When I have green test notification hide automatically after few seconds but When my test have errors I have to click on error messages to hide because they are overlay all other notifications.

How to setup autohide for errors??

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Solution

I'm using Arch Linux. The following worked for me:

Add on Gemfile:

group :development do
  gem 'libnotify'
end

Add on guard file, inside "guard :tests do":

 notification :libnotify, :timeout => 1, :transient => true, :append => false, :urgency => :low

run bundle install again, restart guard, and it works.

Perhaps gnome 3.4 don't hide critical notifications.