The only way to maintain a currency peg is to either defend it with foreign exchange reserves or deflate your wages and prices to accommodate it. To defend a peg you need lots of foreign currency so that when your currency loses value (as it will if you are trying to keep up with the Germans), you can sell your foreign currency reserves and buy back your own currency to maintain the desired rate. But if the markets can figure out how much foreign currency you have in reserve, they can bet against you, force a devaluation of your currency, and pocket the difference between the peg and the new market value in a short sale.

Mark Blyth, Austerity, loc. 213