Submersible powerheads and heaters ???

[IluvHockey]

I have bought an Aquaclear 802 power head and a visitherm heater. These twoproducts are suppose to be hermetically sealed and are totally insulated from water damage and electric shock. But are they??? I see some pictures from the gallery that some people fully submerge thier PH and heaters. However I see do not immerse lines on these power heads and heaters that say not to submerge them pass these points. What do most of you guys do. I don't want to fry myself before I start, especially playing with saltwater.