At the title screen, press Up, Up, Down, Left, A, Left, Right, Down, Down, B and press Start. If done right, the screen should change to black. Now start your game and press Start to enable fast movement and Select to disable it. This cheat, when enabled, will also disable any random encounter in any area - however, keep in mind that this is strictly for random encounters. Any encounter made by touching someone in the field or by a forced battle will still occur, and, as you are disabling random battles, you may be very underleveled, so beware.