I've been working on this cake for hours and a bubble formed and the fondant detached from part of the cake. I tried to smooth it over but it cracked. I don't have enough materials to start over.

slap a bow on it — stick a few flowers on it — in an inconspicuous place, poke a hole into the cake for each layer in there and keep the hole open so no more trapped air will cause a problem — like poke the hole/s upward into the cake so it’s not totally noticeable —

you could put a plaque over it and write the inscription on it 

Exactly as -K8memphis said!  When I first started decorating cakes, I had a friend, who had been decorating for over 30 years, tell me that when you have a booboo, turn it into a feature.  What -K8 is describing is just that.  It has been a life saver many times.  

Agree with all of the above!

But also:

https://www.cakecentral.com/tutorial/61810/the-fundamentals-of-gunging