The correct spelling of "are fence" is actually "our fence." The pronunciation of "are" is the same as "our" in English, so the confusion may arise from the way it sounds. The IPA transcription for "our" is /aʊər/ which shows that it is a diphthong or a combination of two vowel sounds, /aʊ/ and /ər/. Therefore, when we say "our fence," we use a single syllable with two vowel sounds to create the sound /aʊər/ in the word.