Certainty is enjoyable. It's wonderful to be able to describe an expected result as a 'shoo-in'. Don't ruin the moment by spelling it incorrectly and writing 'shoe-in'.
Picture: Paolo Camera
Here is the definition of shoo-in from the Macquarie Dictionary:
shoo-in a certainty to win a competition, election etc. [from earlier US shoo-in a fixed horse race]
Despite the racing connection, there's no connection between 'shoo-in' and 'horseshoe', and assuming there is will only lead you to use the wrong version. So learn the correct spelling. Accuracy matters.
Lifehacker's Mind Your Language column offers bossy advice on improving your writing.