The reason grasshoppers are so hard to deal with is because they can jump and fly. This allows them to go in and out of your garden as they please. Pesticides aren't very effective because you'll only be able to kill the few that happen to be in your garden at that time of application. It does nothing to stop your neighbor's grass hoppers from maturing and feeding on your plants.
Birds and mantis are your safest options when trying to bring the population down, but they won't irradiate them all. However, rarely will you actually lose a plant to them. They don't attack stems like hornworms. They just chew on the leaves. I've tried DE, Sevin, neem, pepper based insecticides, Safer insecticidal soaps, etc and they do great at keeping aphids and small insects away, but nothing really works on grass hoppers. Sevin 5% dust kills them on contact, but doesn't do anything to control their population, so more always keep coming and it's not safe to use Sevin more then a few times a year.
I've learned to ignore them for the most part. Every morning I just go out and shake the plants, pick by hand, or use ice cold water in a spray bottle to knock them off. You can't prevent or irradiate them. For what it's worth, I've never heard of anyone losing their crop (be it cannabis, corn, or whatever) to grasshoppers in regular numbers. Locust however, are another story. God help you if you have locust.