I use:
synclient TapButton1=1 TapButton2=3 TapButton3=2

in order to allow me to use three finger press as a middle-button click on my ASUS UX31A ultrabook. I got this tip from various posts.

I tried to make this persistent and automatic by including it in the "Startup applications" but it is not working. Furthermore, if I run it from a terminal, it stops working if I close the terminal window.

I do not understand why I have this problem and how I can make it automatic?