I'm Bronze Protoss and I have an issue with losing lots of workers to harasses – either pure air or drops, usually not long after 1st expansion.
Being Bronze I only have one strategy – cannons on the mineral line (when I remember to do that) and maybe I leave a few stalkers behind too.
What options does a limited skill player like myself have? Should I continue with cannons and work on more aggression? How many defender units (if any) should I leave in my main and natural expansion? Any other advice on how to better protect my economy?
Best Answer
Try to have vision of your entire base. Place Pylons at the edges so that you know when a drop is about to happen. Keep an eye on the mini map.
This should give you more time to react.
When a drop happens and it is clearly targeted at your workers and potent enough to cause major damage evacuate. Just select all of your workers and move them away. At least momentarily. The short time that you don't mine is easily made up by saving most of your workers. Workers (unlike your gateway units) take a lot of time to built! Make sure your workers are on the way to safety and then get your army to defend against the drop. Once the drop is cleared don't forget to get your workers back to work (and don't forget to put them back on the Vespene too).
If the drop is small and early in the game you may also attack with your workers directly. For example if there are a couple Zerglings or a few marines and I can surround them with my workers I usually do. Later in the game this is usually not such a good idea since upgraded Zerglings or Marines with stim-pack can really cause havoc on your workers.
Scouting is another thing that is crucial in any game and it can give you good hints how likely worker harass will be.
As a Protoss player your army is better if you have them together. I wouldn't recommend leaving parts of your army behind. If you know that a drop is very likely, placing a cannon or two is more cost effective than leaving units and is also a safeguard against any cloaked units harassment (Dark Templar/ Banshee etc.).