Thank you @tommor for a quick reply. Here are my answers to some of the questions:
Based on what I read from currency analysts, Fed is aggressively raising interest rates over the next few years and the Australian central bank is not. So I guess it is quite unlikely that Aussie will get a chance to bounce too much higher.
Based on the above, I fearlessly open short positions (may be too heavy, I lost all my money 10 years ago for the same reason). I close them whenever there is a $50 profit (for each regular lot). And every time, Aud bounces a little higher, I short it again.
Honestly I don’t know how much longer this can last. 70cents to 1 Aud seems to be pretty cheap already. I doubt it can fall below the high 60s. But the greenback has two more years of rising interest rates, it is very uncertain what is going to happen in a year from now. For the next 3 months, I guess shorting Aud is still ok.