Comment 3 for bug 643145

I also had this issue with my dual monitor setup in both Ubuntu and Linux Mint and was able to fix it with a quick code edit in the main guake.py file. I figured I would post it here to help out anyone who may be having this issue until the devs implement a way to manipulate the width the 'Preferences' GUI.

In the meantime this should work nicely and like I said will only take a minute of your time to accomplish. The version I am using is 0.4.2 so the line numbers and exact location of the function may be different for you. A quick grep or search in a text editor should take you right to it though. Anyway open up your local copy of guake at /usr/lib/guake/guake.py in your favorite text editor and find this function (lines 810-836 for me):

def get_final_window_rect(self):
        """Gets the final size of the main window of guake. The height
        is the window_height property, width is window_width and the
        horizontal alignment is given by window_alignment.
        """
        screen = self.window.get_screen()
        height = self.client.get_int(KEY('/general/window_height'))
        width = 80
        halignment = self.client.get_int(KEY('/general/window_halignment'))

The function is actually a bit larger but I've truncated it here to save space. At any rate the string we want is 'width= 100' and as you can see I have changed mine to 'width = 80'. I picked 80 as an arbitrary number because I figured that it would be about right percentage wise and indeed it perfectly trimmed guake to fill the left monitor's space without bleeding over onto the left monitor. Of course you may have to tinker with the percentage a bit to get it right but it should work nicely.

Hope this helps.