Pool Fences

So I left Jon and Anna with my Mom to get an adjustment yesterday. I came back and my Mom was very upset. Here's what happened: My Mom had the kids on the patio and went in the house to get her swimsuit on. Jonathan apparently decided to open the pool gate (the supposedly kiddy-proof one; the ones that cost a ton of money?) and when my mom came back, Anna was in the pool, playing on the island. My Mom freaked. Understandably. The thing that baffles me, other than that we have told Jonathan over and over and over again the he never to touch the pool fence, is that my kids had just finished a very expensive private swimming lesson. I watched them sit and listen intently to the instructor teach them all about water safety. Yesterday was one of those times where I just watched my kid flop and fail and blow it. I watched my parenting in action, all my efforts and hard work to try and teach him the right way, and I just felt like a failure. How will he act when I am not around to tell him what to do? Like when he's at school, or when I leave him at Grandma's house. Will he make me proud, or ashamed?
He intentionally disobeyed us and put himself and his sister in real danger. And my Mom, he almost gave her a heart attack. The day before yesterday I had the kids in the pool. I turned my head to talk to Ed for maybe 30 seconds? Jonathan started shouting Mama! Mama! He was so flustered he could not even sputter anything out, but when I turned to look, Anna had slipped out of her water ring and was flailing around under the surface of the water. How many seconds passed before I could get in the pool to get her out? Maybe 10 or 15, at most? But it felt like an eternity. It was like a bad dream where I needed to run but I could not get my arms and legs to work properly. She was okay, basically, but I can't stop thinking about what could have happened, and kicking myself for turning away. Jonathan immediately said, I think we should just go inside now, Mama. He was totally pale and he said, I was so worried about Anna. He really got it, he really seemed to understand how serious this was. But then one day later, he makes this bad choice.
What was his punishment? We packed his Transformers, his Legos, his GameBoy and put them in Dave's trunk. His computer was turned off and he has no computer, Webkinz, or video game privileges. I canceled a birthday outing on Friday to Pump It Up. He can't go swimming except for his lesson on Thursday. His punishment ends Saturday. Normally, I am pretty lax, but he really needs to know that this is a very serious thing! My Mom called this morning and petitioned on his behalf, saying, I was thinking, maybe you really shouldn't take all those things away. But there is no way we can go back on what we said now. The funny thing is, Jonathan knew he was in big trouble. I was so upset I called his Daddy home early so we could figure out what to do. He was to come in and sit down on the couch and don't you dare get up!!! I think by the time we told him what we had decided, he was so anxious that he was relieved. He probably thought we were going to beat him or make him sleep outside or something. He was very solemn about his punishment, and did not cry or have a fit. He just seemed to accept it.
PS There is just a very small part of me, and no one tell Jon this, that is a teensy bit proud of my clever son. He is just very mechanically inclined, as his Poppa Ed said yesterday! He is just too smart sometimes. I just have to learn how to help him channel his genius, to use it for good and not evil.