Nothing says you can't have inflation in a commodity currency (gold from the new world famously did so after all) or deflation. Nothing says the "value" is constant or not arbitrary or anything different from the perceived value.
That's not how it's supposed to work under the old "gold standard" that tinfoil hatters worldwide espouse a return to. Under the old method, you would peg your currency at "$4.75 = 1 ounce of gold" and that was expected to never change. Ever. Otherwise, what's the point if I can say a dollar is worth .00075 oz of gold today and .0008 oz. of gold tomorrow? Because that's pretty much how it works in the open exchange market today. Currency values fluctuate, the price of gold fluctuates - who cares if you can't force the government to give you gold for that dollar bill when you can always find someone to sell some gold to you in exchange for those dollars at the market price?
And the thing that caused everyone to get off the darn gold standard in the first place was not only that you could have inflation or deflation, but if you had deflation or inflation, there was nothing your country could do about it. And if you are deflating and you can't do anything to stop it, your economy is f$%&*ed.
Aside: For those wondering why economists are so scared of deflation, it's because it destroys the rationale for people to save and invest. If it costs $1 to buy a Big Mac today and will cost $1.10 next year, instead of just sitting on my leftover lunch money I should put it in a bank or invest it so that it makes money and I have enough cash for next year's Big Mac. If next year's Big Mac only costs $0.90, then why risk investing it? I will just keep it under my mattress and I have "made" money (more purchasing power) by doing so. Money in mattresses = banks have no money to lend to people who want to buy houses or start businesses = fewer jobs = vicious cycle of economic misery. This, by the way, was what clobbered the world economy during the Great Depression (along with all the banks that collapsed and ate everyone's savings account, making everyone very nervous about putting their money in the bank).
And there's no such thing as "not enough gold". If you moved the world to a gold standard overnight and we pretend that the world economy doesn't collapse then there's enough gold - the value of gold relative to everything else sky rockets of course. And you use a use a representative currency not actual gold coins of course.
Even that doesn't really work though. In Rand Paul's Good Old Days of the Gold Standard, when the world economy was probably 1/50th(?) of today's size but the supply of gold wasn't all that much smaller, you could walk into a Federal Reserve Bank with a non-ridiculous amount of bank notes and walk out with enough US-minted gold coins that you could trade it or do something meaningful with it. If we tied the world economy back to the gold standard at its current size, it might cost you $10,000 to get a big enough slice of gold that it wouldn't just disappear if you sneezed. And if gold is only useful in gigantic transactions far above the amount of cash most people can afford, what's the point?