As noted the stop loss really can be set where you think the market is telling you that you were wrong. I would only do a mental stop loss if you are trading something that is very spiky. If you are saying right after u get stopped out then the market is moving in your favor, the solution is to use a wider stop loss.
I use 2 ways to protect my position: - If I am able to follow a new trade for a few hours, beeing near the computer, and if the trade is in the green, I set an SL at entry, - I use an Exit EA (in Metatrader) to close a trade, when my chosen (discretionary) indicator turns direction. This might sometimes be a bit late but experience and stats show, that a fast gap almost always turns back and I stay in the trade. Felix
Some arbitrage strategies work best without a stop. For TF a stop is a must otherwise drawdown can get too large.