That garage door gasket would just peel off it was every scraped against a speed bump. You could make something similar like I did for the front lip of my GF's TC. It serves both function to smooth out the airflow and protect the contour of the lip from getting scraped down from entries/exits and speed bumps, and looks good to boot. Made from 6061 T4 1/8" aircraft aluminum. Got a 2'x6' piece of it for ~$200, traced the lip out and inch wider all the way around. Clamped it down on a table and cut it out using a sawzall and WD40 sprayed on the blade to keep it from caking up. Then used a belt sander with 60 grit and shaped out the waves and smoothed out the edges. Took to the powder coater for some matching white paint to contrast against the gloss black of the lip, then a little custom pinstripping and lettering also done by him. Install was easy, attached to the lip using 10 rivets down each side, then attached the lip to the car. And yes I know there is a slight issue with the grammar. Most don't catch it, but it should be "boys" not "boy's". Took about an hour all said and done with the tracing, cutting, and shaping. Pictures from HIN a couple weeks ago. Camera phone pics I took right after we set the car up.
Anyone can make one and make it look really good with a little time in the garage, now if you want CF then that might have to be bought from a vendor or custom made by someone. I don't know many people that have access to that type of equipment. Also if you decide to go with aircraft aluminum, there is various types and not all are created equal. I choose 6061 mainly for its corrosive properties. Form what I know it is the most resistant out of the choices due to the alloy added in with it. Its strength is middle of the road for using the T4 variant of 6061, could go stronger with the T6 or T651. I opted away from going with 6061 T6 due to the lack of need of it taking huge impacts like a oil pan shield would require, just slowing moving scrapes. Also it is only held on to the lip so it is only as strong as the lip is. I choose to stay away from 2024 and 7075 due to again 6061 having better corrosion resistance. Being that it is going to scraped regularly, even coating it will be useless on the bottom and will be worn off exposing the raw metal, which in turn will be coated with junk form the road and start to rust out.
So with that being said. Try making your own. Much easier than it looks.
I really like how the white defines the edge of the lip. Will be doing something similar on the Z when I get a chance to have some extra cash to order the sunline lip. Here a lower shot taken with a better camera.