Thank you for the replies.
Our two older boys are good swimmers so we feel good about them. Our 3-year old is the concern -- he is very curious and has no fear, a potentially deadly combination. So the precautions are largely for him. He is in swim lessons this entire summer, but I don't expect him to be proficient until after next summer at the soonest.
We are still undecided on the fence vs the net. The net is a little more aesthetically pleasing for us, but definitely a bigger hassle. We haven't completely considered a pool cover yet, but that may be better still given the winter factor. From above, it sounds like a cover over a net might be an option as well? I'm calling Katch-a-Kid today; they do nets, covers, and fences.
Any specific recommendations on an in-pool motion alarm and door alarms? Looks like a company named Poolguard sells both on Amazon and the reviews seem ok for the most part? We're hopeful that with a combination of deterrents and two hyper-vigilant parents, we'll be ok.