I don't think the OP's complaint is that he's getting pooped on, it's that he's getting nailed with poop - and likely pee and musk - every time he handles the snake because the snake hasn't tamed down and likely never will at this point. I have two garters like this and dealing with them is a headache. They're fun to watch but not hold.
This snake would do better in a display-only home, or maybe a breeder would be interested if it was a morph.