cover all bases
To be well-prepared for every possible outcome. We need to cover all bases here—check every office and make sure it's been evacuated. I know I don't have the best grades, so I covered all bases by applying to 15 colleges.
cover (one's) feet
A Biblical euphemism for defecation. (While positioned in that act, one's robe would cover one's feet.) A: "Where is Joe?" B: "Oh, he's in the restroom, probably covering his feet, if you know what I mean."
under the covers
1. Literally, in one's bed. I'm not going out tonight—I'm already in my pajamas and under the covers!
2. In consort with another, usually secretly (and perhaps scandalously). They may represent different parties, but I think those two politicians are under the covers together. The way he keeps looking at her makes me wonder if they're under the covers together.