Lose focus/toggle focus shortcut?

Is there an option to lose focus to switch back to the app prior to guake? Since guake doesn't show on `alt+tab`, there is no keyboard shortcut to switch back the the previous app from guake and currently I have to use mouse for that. Please note that losing focus doesn't mean toggling visibility; the guake window is still there, but I can still work with another app.

I think it would be a nice feature if there hasn't been already.