Go to the split screen map, Guardian, not on Forge.
Grab a sniper or spartan laser, and a grav lift and get to the middle arena area and look to where lots of high logs are standing up.
Jump to the low log that has the bubble shield on it and look to the right.
Jump on the edge, you will see a hollow tree to jump on to, jump on it and then wait, jump up and throw down the grav lift right to where you were waiting and then it should throw you up and you will end up on a higher log.
Then jump to where there is a higher ledge and carefully make your way the other higher ledge and then make your way to the end of that ledge.
Stop then get out your sniper/spartan laser and shoot the crap out of any one coming out into that open area
Have fun Guardian sniping!