Once you got profit then just stop it. Because if you change your profit to a percentage you could control your greed.

it is difficult to think to stop the games once we got profit because our mind will tell us that we can win more money. if we can control our feeling to say it is my time to stop then we can stop right away. every time we win the game, it will make us become greed and if we cannot control our feeling then we can continue to chase more win which we cannot always win.
Because we do not win most of the time, we think this is the right time to win more so we push our luck, that is not good for me because we do not control our luck and we might run out of luck and end out with nothing, that is very frustrating because we experience being up but we failed to make a right decision, normally when that will happen we will blame ourselves and that will affect our future engagement with gambling.