Currency controls (taxing money movements out of a country) have serious problems. Foreign investment would dry up because they won't want any profits or capital gains taxed on exit. Domestic firms will suffer a severe penalty on trying to invest abroad, giving foreign companies that can a big competitive advantage. Buying foreign stuff would become more expensive, so the cost of foreign made goods would shoot up, also the cost of imported parts and commodities for local industries would rocket, killing domestic industry competitiveness. You'd have to also tax assets and goods moved abroad because otherwise people would buy stuff locally and sell it abroad as a tax dodge. Basically your whole economy would become massively distorted.