Look guys, I've done this a thousand times, and they've never pound anything. Slopain is right in that if they really want to find it they will. What makes them want to find it, however, is how you act. if you're a skinny high school kid, they might look at you more suspicously than an elderly man and his wife.
What i'm trying to say is, don't act stupid. Make sure you have a story as to why you're down there. I always go with my girlfriend (which I suggest you do if you have one), and when I come back across, I just tell them that we went to Rosarito for the weekend to party at Papas & Beer. If you have a good tan, bring along a surf board and tell them you went surfing/snorkeling in Cabo. No sweat, right?
Another thing; DO NOT hide your gear/needles/pills in the wheel well under the spare tire. They look under there all the time.
If you're a nervous type, take a valium before you cross to help with the anxiety. Well, that's about all I can think of. Good luck bros!