Replacing light fixture

I am planning to pour a concrete patio. I would like to run two pieces of PVC conduit either UNDER the slab or IN the slab for future electrical lines. I would "cap" each end of the conduit until I find a need to run the lines. What is best? I am concerned that running the conduit under the slab (below grade) would allow water infiltration once I remove the "caps" and run the lines through the conduit. Would this be a problem? I could avoid water infiltration by placing them IN the slab (above grade), but this requires a little more preparation. Any thoughts?

I have been trying to replace an outlet in my kitchen. It is a combination outlet and switch. I went to replace the outlet/switch and have discovered that there are two hot lines coming into the outlet. I cannot figure out how to get it so that both the outlet and the light can be controlled. Whenever the two hot lines are in any way connected (either through the outlet or by tying them together it blows the circuit. Does anyone have any idea how to make this work. It worked before so I know there must be a way but I'll be damned if I can figure it out now. Any help would be appreciated. Thank you.