This claymore trick is useful if you're elevated above the enemies, but only have a claymore and want to set up an ambush, without getting killed. It's relatively simple to do, but works great.

1) Ensure you have a claymore equipped. This is all you'll need to bring with you.
2) Climb to an elevated surface which has a ledge above ground (ie. Sub-base, this has a lot of them. Basically areas where enemies are running on the level below you but you can still see and shoot them).
3) Position yourself so when you look straight down, you don't appear to be standing on anything. An easy way to do this is to align the edge of the platform you're on with the bottom of your TV.
4) Now, simply plant your claymore. You'll notice it gets planted on the lower level.

This is particularly useful for confusing enemies who continually spawn in the same area. If you use with OMA, for example, you can sit on one of the two elevated platforms, on Demolition, by the Spetsnaz spawn then plant a claymore right at the corner so anyone who runs by gets foobar'd. Then simply use OMA (one man army) to refresh your loadout and repeat. Few people should see you if you move away from the edge so you can do this over and over!

I've attached a diagram of where I'm talking about if you don't know.

Lol, neat. I knew about being able to play claymore on the floor from an elevated position, didn't think to use it in this way though, it has potential!