I guess most of you (including me) would like to lock their screens. You accomplish this in Openbox by installing and using XscreenSaver.
sudo apt-get install xscreensaver
sudo nano /home/YOURUSERNAME/.config/openbox/autostart.sh
#ad this line
xscreensaver -no-splash &#save and exit
sudo chmod +x /home/YOURUSERNAME/.config/openbox/autostart.sh
Adding an entry to obmenu
obmenunew item ==> label: lock ==> action: execute ==> execute: xscreensaver-command -lock
save the menu & exit
You should now be able to lock your screen.