Stop Snakes Invading Purple Martin Houses

Although my mom still uses some netting over her strawberries, the majority is wrapped loosely around the base of her Purple Martin houses and is tied in place as soon as she raises them in the spring. So far this year alone, she has caught six chicken snakes in the netting. No snakes have reached the birdhouses. I also put netting around the base of my two Purple Martin houses, and within one week a snake became entangled in it. It was dead when I found it. The hardest part of the process seems to be killing the snake (pruners and loppers work okay) and then getting the snake out of the net. Their scales prevent them from being pulled back out, so we've had to cut netting just where the snake was caught.