I find that using sense and someone goes force active in your vicinity you will pick it up...like quigonn seeing anakin racing and subconsciously using the force and then testing more. If a Jedi isn't actively using the force it should be very tough to locate
The average Clone Wars era Jedi have been taught from a very young age to use the force. It's ingrained in them so much that just switching it off can't be that easy to do. Even Luke's rudimentary training gave him away to Vader ("The force is strong with this one").
I read the Darth Plagueis book recently, and (though it's hardly canon) it described Palpatine as having been trained to mask his presence in the force. Which makes a certain degree of sense to me. I mean, he is obviously a very powerful Sith, but he just stands around Quigon's funeral pyre with the Jedi council looking on and nobody feels anything?
Maybe the shroud talent someone mentioned is supposed to represent this, but it sounds like it's too restrictive (once/session) to be of any real use.
Edited by papy72