We had a pool at our first house. At that time we didn't have children but had young nieces and nephews who would come and spend much time with us. We had a lock on the fence from the drive way-a lock on the the garage door that housed the pool filter, and we had a gate on the back deck that had a lock. Unless we physically undid the locks they couldn't get in the back yard, or near the pool. They also learned very early that unless we were on the grass that they weren't to be in the pool at all ever. Its like anything else--you have to teach them.