Are you saying you want to add an additional decorative border that's different from the rest of the image, or do you want to expand the image so that the monkey's yard and sky are larger? (i.e., drawing more yard and sky around the edges?)

If it's the latter you want, then the just enlarge the canvas and go to work on it with copy/paste, invert selection, and liberal application of the clone tool.

Attached is only about 5 minutes' worth of half-hearted screwing around, to give you an idea of how to do it.