How can you stop poaching?

You could report any suspicious activity you see to Fish and Game. Other than that there's nothing else you can do.

Use cheap trail cam's in places that poachers are likely to shoot from if you are trying to protect a specific area.

If your trying to drive off road "hunters". Simply take a camera and follow them. They are allowed to drive on public roads but so are you as long as you follow traffic laws. After you prevent them from shooting a few times they generaly go find less protected areas.

Either way photos or video's of them tresspassing or shooting from the road need to include a timestamp and identifyable features.