I trade with TD Ameritrade. They have an order called aTrailing Stop Order, where you can enter a buy order whiich is to become active at a specified amount above the current price (simplifying a bit here) or a sell order which is to become active at a specified amount below the current price. The trailing part of the equation is that the activation price for a buy TS Order will fall if the current price falls - (and vice versa for a sell TS order.)
However, they require an open position in order to place one of these orders. Why? If I want to buy a stock which is trending downward, wouldn't it be useful to place a buy TS order, say 1% above the current price, knowing thast my activation price is probably going to go down if the trend continues, but that if the stock starts an upward rise, I will have my order placed 1% above the lowest point the stock reached.
I could see placing a lot of my orders this way as One-Day orders. Why is this not possible?