You can't really stop him from hearing the songs. I was also very cautious with my choice of music. I listened to more easy going music when she was young. I also checked most of her book choices, and movies too.
Growing up, we had music that has inappropriate lyrics. I actually didn't understand most of those songs... even though I thought I did. I listen to them now, and think "Holy cow.. THAT'S what it meant?"
But, movies and books had a much bigger impact on me. I'm still traumatized by movies I saw as a kid. "Soylent Green..... is people!" I still haven't recovered from that one.
I read a book that I bought in the young adult section when I was 13. It was about incest. I thought it was about a brother and sister having the whole summer to dig a fort in the yard, when it was really about incest.
But, most of the music, went over my head. So, it never left an impression on me. But, if you are uncomfortable with it, keep your radio on a channel you are comfortable with, and don't bring too much attention to lyrics when you don't like them.