Google for "USB charge only adapter". That's a little adapter that you put between your USB cable and the computer, and it removes all the data lines. It is now impossible for any computer to communicate with your phone AT ALL. The "Trust / Don't Trust" will not come up, it's just as if you plugged your phone in a charging port.
Of course it also prevents you from accidentally connecting to a computer. So if you connect to my computer, there will be no danger that your phone creates a backup on my computer, or takes its music library from my computer. So some people buy these adapters for their computer, to prevent random phones from connecting.