A timely reminder, if one is needed, of the stupidity of introducing controls on financial market flows has been provided by Thailand recently. While this is an extreme example, with absurdly restrictive, indeed punitive, restrictions introduced in haste by a government that is inexperienced and, in financial terms, ignorant, it serves to show yet again that interrupting capital flows to try to manage the currency is just plain folly.
If your currency is changing in value more than you think is good, work out why it is happening. Then change that. You will normally find it is due to wrong policies in another area anyway.