I was recently challenged to learn a new English vowel. This Auburn dog or sound. Currently, I use this olive sock or sound. It's not random. I wouldn't get to Auburn or some words and all of all other words. I need to listen to people who use both of these sounds in English and keep track. Which words have that olive or and which words have that Auburn or sound? Then double check using a dictionary. Focus on my pronunciation for words with that or like caught. Get used to people's reactions every time I pronounce words with this sound. I'm guessing. This is what you go through. Every time you learn a new sound of English.