Stop smoking. You eye is red from smoke entering the eye itself through the air. So smoke in a well ventilated place. A few get red eyes from the chemicals in the smoke which can dilate eye vessels internally. If that is the case you need to stop smoking. I am guessing you are worried that the red eyes are a give away to your weed habit. So don't smoke when that would be a problem.
Just say no... Just don't smoke weed to begin with.