Plateau base defence
Park by the rock group located at the bottom of the steep right path up to the plateau. From there you have a good view of a longish expanse of ground with a rock in its midst. It doesn't take the enemy long to start swarming in, so you better get ready quick. Try to fend them off. Normally I'd drive in past the lifeboat for this plan. Most enemy are likely to attack from the front, but watch out for others sneaking around the cliffside and coming in behind you from either direction.
Positioning
As with most situations, you can have fun trying out different defence positions. For a bit of a crossfire you could park the Warthog to one side of the rocks then position yourself on the other, but that does leave the hog a bit vulnerable to surprise attacks from behind. If you're on the left, you're well positioned for tackling any Elites that followed you around the cliffside.
My first megabattle experience!
Aside from giving some fantastically hot combat, this plan has a bit of historical relevance for me because it describes my first megabattle experience. I'd returned to the rockslide area after killing the initial covies and then - just to vary my routine - deciding to leave. By now all the dropships had visited, though I wasn't really aware of that at the time. I was probably expecting things to resume from pretty much where I'd left off, with dropships coming in gradually. Anyway, I drove in and parked near the rocks I mentioned, and then all hell broke loose as a mass of enemies flooded my way. I don't think I lasted long; I just wasn't prepared for that sort of attack! I remember thinking something like "What the hell was that?". Naturally I reverted to try things again - and again. It was easily the best fighting I'd ever had, and I was pretty amazed at what I'd stumbled into. Thus began my involvement with the rockslide megabattle, which eventually led to my launching Bad Cyborg.
Actually I almost called the rockslide megabattle something else. My original name for it was 'secret rockslide scenario', which I was going to abbreviate to SRS. But I did a web search and found that SRS was already the initials of something. I didn't want to clash, so I had a rethink. Glad I did, because 'rockslide megabattle' was much better, and 'megabattle' later came in handy for describing a few other super-intense conflicts.