Congrats on trying this, giving it a go without a cage first is a great idea!
So, how to prevent him going over… it’s a serious problem actually and we battle with it too as personally, while I love ruining him occasionally on purpose, if I didn’t plan it it’s now annoying. Yes he stays hornier than if he’d properly cum, but it definitely drops his arousal back down and his balls aren’t as full anymore.
So first let’s agree a principle. It is ALWAYS his fault if he goes over the edge. Why? Because you’re not psychic, therefore it is his job to tell you to stop or slow down.
There’s a few approaches I’d recommend trying:
The first is training.
Deliberately spend time where you’re not worried about him going over, but playing and and learning to communicate better so he can tell you, and you learn from his body language, when he’s close. It doesn’t matter if he goes over but, you still ruin it anyway as it’ll keep him horny and you can try again maybe.
Some guys can be ruined multiple times in a row!
Also with the practise, explore ways to stop him ruining as he goes over the edge. The most famous is sliding your hand down to the base of his cock and squeezing REALLY hard. Another is trying to give it a slap!
One for him to try is squeezing his kegel muscles (are they called that on guys? anyway, the ones he’d use to stop peeing) and he has to tighten them really hard and HOLD it.
Now going back to our principle that it’s always his fault. If you really get that into your head then this second approach becomes more acceptable. Teaching him not to ruin by punishing him when he does.
Basically you’ve got to get him in a mindset where he honestly doesn’t want to cum because the payoff isn’t worth it.
The classic one suggested is that you make him eat his cum if he ruins without permission.
The trouble with him eating his cum is that, while he’s horny and on the edge, he probably gets a bit turned on by the idea. Yep! It’s true! So it’s not actually a great dissuader at the point it’s needed! Still worth trying though (again, any reservations just think about how often he’s wanted YOU to swallow it! Focus on that and it becomes strangely satisfying and amusing.
A better punishment is some lock up time (if you use a cage) where he’s not allowed out. That’s what we do at the moment.If he ruins without permission it’s three days without release.
But last is pain… namely, if he ruins, or have an allowance, if he ruins more than once in a week, he gets menthol rub all over his cock and balls as a punishment. I use that as I’m totally not into impact play, but obviously if you LIKE the idea you could spank him or cane him or whatever. For some reason I’m okay with penis torture but any corporal punishment is a turn off (well, giving it to him, I love getting it! lol)