Using an asset as debt-collateral triggering gains being realized would be good too. As would unifying the income and capital gains tax.
I disagree with TFA's idea that a wealth tax is the best solution. IMO wealth is easier to hide than income, it's just that nobody bothers right now with there being no wealth tax.
It sounds trivial but the effect to various tax evasion strategies is very important. It's also something that really ought to be uncontroversial. Read the book!