Por favor que se detenga!
Is this the best way to say please stop, like urgently? The que makes it subjunctive? ( I have no left way to make a lef one)
This is another one of those indirect commands, and - as such - it isn't as urgent as "deténgase" or "detente".
What you have is more like "please, stop" and not "stop!"
I would say, ¡Párese!
There is no need for subjunctive with imperative case.