Next on most people's list of tools is a heart rate monitor. Remember that heart rate takes about two to four minutes to fully respond to a set workload, so it's essentially useless for short events of less than six to 10 minutes as a pacing tool.
In longer time trials, remember to not gauge your initial effort on heart rate, because you'll be going too hard if you try to peg your initial pace to your lactate threshold heart rate, and will end up paying for it later.
As with all monitoring tools, ultimately the important thing is that they help you fine-tune your self-knowledge about your capabilities. Therefore, perceived effort should also be used to monitor pacing. However, such self-awareness typically only comes after using monitoring tools diligently for a long period of time, but it's still a valuable goal to keep in mind as you use other tools.
The Plus Side of Negativity
The advanced pacing technique that is most difficult to pull off is known as doing "negative splits." This is what coaches mean when they say to start slow and then get faster as you go. Essentially, you break the distance down into segments and try to increase your pace a little each segment.
This is very difficult to do because it takes an incredible amount of discipline to avoid going out at max effort (you feel almost guilty because you're not killing yourself), and then to be able to kick it up a gear as the event progresses despite accumulating fatigue.
Probably the greatest example ever of this strategy was the Norwegian speedskater Johan Olav Koss in the 10K event at the 1994 Winter Olympics. In his home track in Lillehammer, Koss started off at an insane pace that was already faster than any other skater, then managed to systematically do faster and faster split times for the 25 laps throughout the entire 10K.
If you're going to do negative splits in your event, it is essential that you scout out the course (if a road event) and plan your effort. This is where a CompuTrainer and its mapping and course-creation software can be a huge benefit, allowing you to really get familiar with the course and the effort required.
You have to know your pace for each segment, based not just on your present condition but your ideal condition on race day. In practice and in the race itself, this is one situation where a power monitor is of overwhelming benefit, because perceived effort and heart rates are likely not sufficiently sensitive to these minor tweaks of your workload.