Karen, the apartment situation sounds like a lifetime worth of nightmares! You can buy a snake repellent at most home centers, like Home Depot. Snakes are often attracted to water, like the baby pool you may have already filled in your backyard.
I was always told that lawn fertilizers repel snakes, but I have seen several in my yard, including a very large black snake. We have very few poisonous snakes here. I'm not sure about your area.