It's true that under a more or less constant money supply prices would go down due to improvements in production. However
-gold is also subject to improvement in production and its production grows along with the rest of the economy.
-even with money constant and prices going down fast, it is not any different in managing from prices going up. Prices of computers have been going down since the dawn of time, but people still buy them and invest in their production.
Sure investments are more easily made if business men know that the money is worthless in a few years, but this is not an advantage for the allocation of resources. Their needs to be risk in investing otherwise the foolisch would start businesses counting on inflation to pay back their loans. They take resources away from better use.
If falling prices would scare businessmen from borrowing for investments, new investments would not come and prices would stop going down. The loans also have to payed back from the margin times the volume. In a free society with a constant money supply, it is likely that wages are falling as wel (money constant and population growing), but as productivity increases, you might earn 2% less money and buy 6% more goods. I think this is what was happening during the gold standard at the end of the 19th century in the usa. This period is now known amongst statist economists as horrible because of deflation, but purchasing power grew considerably (and that is all that matters). Keep in mind the proper definition of deflation is not prices going down, but a reduction in the money and credit. So allthough prices were going down steadily, there was no actual deflation, since the money supply grew moderately.
The course of G Reisman on capitalism explains it much better than I do, including examples how the repayment of loans is not in danger under falling prices (it is a problem to pay back loans if the money supply decreases though, which is the case under current boom bust expansian and contraction of credit policies). How the reasoning behind this exactly went, I forgot. I think it was something along the lines of: if money supply remains the same and the velocity of circulation, the volume of spending stays the same. This means business men can tap into the same amount of spending going on in the economy to repay their loans. When central bankers however get scared of inflation and slam the breaks (and contract money supply), the volume of spending actually goes down and there is less money to tap into to repay loans (just as the preceding inflation boom encouraged them to increase borrwoing)
Other currencies than gold could also be possible in a free society. They could inflate to keep prices constant, although it would not be directly clear to me who would get the benefits of the inflation.
Does this help?
Violence has nothing with which to cover itself except the lie, and the
lie has nothing to stand on other than violence. Any man who has once
acclaimed violence as his method must inexorably choose the lie as his principle. Solzhenitsyn, Alexander