What's to keep your condom from breaking during sex? Your wife from cheating on you? Your house from catching fire?
Maybe he should be made to take a class in holding a conversation before he started talking to you? Or perhaps a class for crossing the street? Maybe one for living your life without taking training classes?
Life is not 100%, ever. There is no way to be 100% safe all the time, even with training. Special forces operatives die all the time, as do SWAT members, etc. And they spend hours upon hours of training.
My solution to stopping a gun grab? "Suicide" flap holster. A lot of people say they are slower than other holsters but I haven't noticed a big difference in draw time once I got used to it. Once you've gone through the motions enough you get quicker and quicker. There is absolutely no way someone is going to be able to get behind me and grab my gun. It also works if you're OCing in the rain, the only thing getting wet is the handle, which is plastic so no biggie.