Getting an ocean monument to generate
I've used some tools to determine the location of the new 1.8 ocean monuments on the UMS. I checked by going to the coordinates - the guardians are there but no ocean monuments generate.
To guarantee that an ocean monument would generate I propose the region file concerned be deleted. It is r.3.2.mca, and if you look at the top down render of the specific region (http://ums.pixub.com/topdown/tile.3.2.jpg) it's composed of mostly ocean, and doesn't seem to have anything manmade, so I suppose it's safe to delete and regenerate the region - with the ocean monuments.