I have a 2006 Scott plasma pro cr1 tri bike. I have a problem with the cable housing for the shifters in that the cable housing won't stay in place. I bring it to the bike shop, they fix it and 2 weeks later it comes off and i can no longer shift. Is there a trick to keeping it in place and not going into the frame?

That makes zero sense.

You should ask your LBS (if you're even describing the problem correctly) about your concerns. I'm going to assume you're talking about cable "stretch" after initial installation. If it's "stretching" enough that your cable and housing fall out, your LBS has idiot mechanics on staff. Other than that I can see no reason why properly cut, finished and installed housing should jump out of stops like that.

There is nothing unusual about the routing (no different than any other internally routed shifter cable) on your bike.

ok thank you. i thought that internal routing systems had a different way of holding onto cable housing. I fixed my problem geez it was so simple.

maybe there is a defect in the housing. like a pinch or crimp that causes the housing to follow the cable movement?