Jedd, it was a joke!
I have the Fenda Extenda too. I did remove the fender for Fenda installation (see what I did there?

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It is easy to remove and reinstall. By removing it, you will be able to properly clean the inside surface so whatever adhesive you use will bond properly. Personally, I cleaned mine and then wiped it with acetone to remove any grease. I may have roughed up the inner surface some too. I did wipe the Extenda surface with acetone to deglaze it, and then scored it some to aid in adhesion. But, I tend to be a little anal sometimes. OTOH, it's been on there 3 years and is fine.
A number of us have used different stuff, like the JB above, some epoxy,etc. I used marine 3M4200 or 5200 (can't remember) and clamped it until set. Comes in black or white. I would advise against using silicone.
Done nicely, it will look just like the above pic and will last forever.