You could buy 10 calls on FXA (the Australian currency ETF mentioned by Hart CO) expiring in 12 months. Each share of FXA approximately tracks the value of AUD100, and 10 calls correspond to 1,000 shares.
The choice of strike price is a tradeoff of how much you want to spend on hedging and how much risk you are willing to take. A higher strike costs less but AUD would be able to rise more at your expense before your protection kicks in.
In your scenario, you face a real problem: If you have little money to spare (which can be presumed since you're resorting to borrowing, and in a foreign currency at that), you fundamentally don't have much room for error if AUD rises sharply. You are funding your US business by effectively taking on a large AUD short position, which is not really a good idea in the first place.
It would be preferable to find a way to borrow in USD for your business.
Trying to hedge AUD using plain ETFs or futures, without options, can lower your cost in theory but ultimately relies on the ability to borrow in USD (and if you can do that, why mess with AUD at all?). To outright buy 1,000 shares of FXA would cost you the entire amount you borrowed.
To buy a futures contract on AUD 100,000 would require only a fairly small margin deposit up front, but then if AUD goes down, you have marked-to-market losses and have to put in more money. Where does that money come from if you put everything into the business? Maybe this works if the business has some divisible assets you can quickly sell off for cash, and then you end up with a smaller business but a lower USD value of the debt.
