There's no sure fire method of beating an opposing defender towards the higher difficulty levels...yep.
However, the L1 button is your best bet.
BTW, how do you do that short dribble thing? It's not always 100% with the L2 button. You touch it with ur left foot, then immediately, stretch ur right foot out and tap it again, causing time to make ur next move, and throws the defense off if the second touch is at the right time.
Also, i've kinda mastered the dummy technique. If you pass teh ball to a temmate, and you see another player in a better position directly behind them or in the direction the ball is traveling...hold down R1, and your player will split his legs, allowing the ball to go through to the next player. This also works great, if a defender is charging at the player who is about to receive the pass...like in real soccer.
And finally, the stepovers...I've figured out two ways to make them work. I use the step over, then immediately the shot fake, and that sometimes helps you get by the defenders, and it looks "Rivaldo"-esq. Also, do a step over right before you take a shot...I don't know if it works, but it works a lot better for me. I've tried it in training. When just shooting on a run up, goalie will make a quick guess...but when i step over, then immediately (i mean immediately) shoot it, the goalie seems to react too slow...perhaps that's just my game. But when a defender is on you, do the stepover, and immediately pull to the sides...that's the only way it'll work at all. I only use stepovers to make the game look more realistic...especially if i'm Brasil