Anecdotally, I use xidle[0] and xlock[1], and have found both to be very reliable. xidle supports locking the screen by sending it SIGUSR1, which is really useful since you can trigger it from a process that doesn't have DISPLAY set.

The trick on laptops is to block on sending the signal in the script you use to suspend, so that when the laptop resumes the display is already locked.

0 - https://github.com/steinex/xidle-linux

1 - http://sillycycle.com/xlockmore.html