I completely understand your desire to avoid sales of your long term investments that may have huge capital gains. To deal with that, you can configure us to sell shares in a tax sensitive way, where we will sell shares with a low tax burden first, so if you have a greater inflow into your account than outflow (which would be the case for a SDE DINK), we will usually just sell recently bought shares that haven't accumulated any capital gains, and all the shares with a high tax burden will never be touched.