I recently bought my first house and I noticed some rot happening beside our garage door. It appears that when the cement driveway was poured, they got too close to the siding and now water is wicking up into the wood. I figure I can cut back the siding and replace it but how do I stop this from happening again?
With epoxy-based putty or paste. Take a tool and dig out as much rot as you can. There's a two part epoxy you can get that goes on either as a paste or a putty.
For the paste, you'll need to build it up over a few coatings. For the putty, you can form it like play-doh.
Use batons to form it or get it in rough shape and then use planers, very sharp chisels and/or sandpaper to shape it. I typical do the shaping when the epoxy is not 100% cured but rather, 60%-80%. Easier to shape.
Once in the correct shape, allow to cure and paint.
Don't use liquid epoxy. Unless you have a 100% fool-proof seal, you'll make a mess. Hell, you'll probably make a mess even with one.
Good luck!