Review the item:
Derek wanted a ferocious pit bull terrier to scare off burglars, but his
apartment complex did not allow dogs as a result,
Derek had to settle for naming his goldfish Mr. Jaws and installing
additional door locks.
As a result is a prepositional phrase. Derek had to settle for naming his goldfish Mr. Jaws is a main clause. You can connect a prepositional phrase to a main clause with a comma.