Countering scout harass as terran
Solution 1:
You have to use another SCV.
That you do is factored into the balance of the game. For gosh sakes man, you have mules, it's enough money.
Edit: I believe Mark's answer is wrong. There's no way to prevent a scouting worker from seeing your build with a SCV and that has nothing to with whether or not you should use a second SCV.