Something that is a sacred cow is held in such respect that it cannot be criticised or attacked.
A shaggy dog story is a joke which is a long story with a silly end.
If you separate the sheep from the goats, you sort out the good from the bad.
If the sharks are circling, then something is in danger and its enemies are getting ready for the kill.
If something is like shooting fish in a barrel, it is so easy that success is guaranteed.
A convenient and superficial explanation that is normally unconvincing is a short horse soon curried.
If somebody's as sick as a dog, they throw up (=vomit) violently.
If someone's sick as a parrot about something, they are unhappy, disappointed or depressed about it.
If someone sings like a canary, they tell everything they know about a crime or wrongdoing to the police or authorities.
This means that eventually you will achieve your goal.