[ct-fiskerbuzz]

I think "lower valence" the correct name for the big section under the rear bumper... in any case, mine seems to be a bit loose, probably after scraping over something.

Is there a good way to make sure it doesn't come off until I can get it properly fixed?

 

[FiskerZee]

Zip ties are possibly the easiest and best answer. Get some industrial strength Zip ties. That should do the job semi permanently and can also be out of view so no one sees them.

 

[Harleyguy]

You don't need any heavy duty zip ties I use rather small ones I drill a very small hole from the piece that's hanging down into the part of the bumper the piece was attached too.
The tie wraps I use are about the size in diameter of a tooth pick

 

[ct-fiskerbuzz]

Turns out it's not loose, it's cracked. Not sure if that's better or worse. :s