There's a reason why that answer at AskUbuntu has 0 votes: the Synaptics driver is very old code, originally a driver for one specific early touchpad by one specific manufacturer connected in one specific way. Over the years it's been hacked again and again to include other interfaces, other devices by other manufacturers and multitouch. Depending on what else you've got in your system installing it can lead to situations in which none of your input devices work. AFAIK nobody works on it anymore and it's probably going to go away in the near future. Had I noticed this answer in there I would have cautioned you against trying it. Nice for you that it works, but that was risky.
Back when I used synaptics - in Ubuntu 12.04, I think - there were additional options available in the mouse settings if you used that driver. Check whether that's still the case, maybe you can just put a mark in a check box and be done with it.
If that's not the case then the easy way to having that setting always active is to put a desktop file in '~/.config/autostart/' which will execute that command when you log in. Open your favourite text editor, cut and paste this block
Code:
[Desktop Entry]
Encoding=UTF-8
Version=0.9.4
Type=Application
Name=Set LockedDrags
Exec=synclient LockedDrags=1
StartupNotify=false
Terminal=false
Hidden=false
and save it as '~/.config/autostart/setLockedDrags.desktop'.
Holger
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