Now, if I remember right, there was a nice little moment in an old Halo novel. Before I start, may I state that, this blows your "Can't see me so ded." statement off to somewhere else. It's known that Covenant cloaking tech is so far, superior to anything humans can make in the Haloverse. For normal marines, Covenant using clocked tech are nearly, and hoplessly invisible. And even for Spartans and their enhanced vision, along with the assistance of their suits, all they ever saw were blurred images, things that didn't quite fit. Several Spartans were holed up in a mine, and couldn't get out because of the cloaked Elites. This is Blue team by the way, el Chiefo's best buds. So anywho, they used old cans of dust, something like talcum powder, and simply threw it over the cloaked Elites, which stick to them and marked them out. Things were relatively easy after that. And, please note, this was Mark 5 armour they were wearing. There's a good chance that Mark 6 has better equipment to pick up cloaked enemies. So basically, cloaking won't save our nano-suit wearing friend. Especially if somebody took a handful of sand and threw it in his general direction.

Mark VI does not have better vision tech. At least, none that we've seen. And they see cloaked sangheili exactly as well as anybody else - that is, all they see is a shimmer. And if the Nanosuit-wearer is cloaked and not running at a dead sprint, the Spartan won't be seeing anything.

I don't think so. We can go back to another novel I believe, when Captain Keyes was being tracked by a Spec Ops Elite. Now, Keyes probably didn't have special vision, but when our spec ops elite got in an escape pod with him and a few other marines, Keyes was the only one to notice the slightly off putting view at the back of the pod. And Keyes did a double take on it, at first he thought it was just something going on with his head. Clearly, there's a difference between what a normal person can see and a Spartan. But yes, if our friend in the Nano-suit stayed still as a statue, it would probably work. It might help if he stayed in an inconspicuous location too. But even still, better hope the spartan doesn't catch wind of him and tosses some sand his way.

As soon as the Spartan bends down to grab some sand, the Nanosuited guy would shove his boot so far up the Spartan's ass it would come out his face. It's been established that Active Camo is not fully invisible. Keyes could see the shimmer. That's it. Nothing different from what a Spartan could see.

You make it sound as if the spartan is elderly and would throw his hips out if he bent down to pick up some sand.

And you make it sound as if the Nanosuit-wearing soldier is just going to stand there while the Spartan bends down to pick up some sand to throw in the direction he/she [i]thinks[/i] the soldier is.

You don't think the Spartan would so easily convey his or her actions do you? I don't think they'd just up and wander over, bend down and scoop up some sand. They'd do something as a cover, or act in a manner that diverted the attention of the soldier, or even provoke him into moving, long enough for them to get a handful of dirt or something.

None of which would matter, because the Nanosuit can muffle footsteps as well as render the user nigh-invisible. The Spartan won't know they're there, and thus won't know to grab some sand or whatever. Besides, nothing the Spartan has would get past the Nanosuit in a straight-up fight, so why would they bother hiding?

Who knows? Spartans are superior to their regular human counterparts in their own verse, but their most powerful and often used tactic is stealth, even though I'm sure if they wanted to, they could walk around guns blazing. I'm assuming that stealth is a more commonly preferred tactic for nano suit soldiers as well.