Is there a way to short Ruble?

This is one of the easiest one-way bets out there. The way Russian Central Bank is devaluing the ruble - there is no two-way risk in shorting the ruble. The bank is implicitly admitting that the currency is overvalued. But instead of having one sharp depreciation, it is only letting it depreciate slowly.  

Now, is there a way for a retail investor to short the currency? I don't want to short the XRU - there is no volume. Besides, I am not really sure what is the structure of these ETFs themselves.