In our experience this age is a very delicate balancing act. He will either start to want to use the potty on his own, or start to want to not use it as a means of expressing his autonomy, if he isn't getting enough of that in other areas, or if you are too eager for him to graduate and he senses that pressure.
It is difficult when we are used to keeping all this poo/pee stuff under control to let go of that control and give it to your son. It will probably mean some more misses for a bit, but if you can just back off from it and let him know, it's up to you now to take yourself, or to let mama know, or even just tell him, the potty is in the corner when you think he might need it, but avoid making it something you feel strongly about at this stage, he will sort of naturally start to make use of his abilities. If he can hold it out of the house, he can hold it at home, but he is either so used to you taking the initiative, or he is using the potty as a way to tell you, "I do what I want!", or he isn't quite at the mind milestone where he has put it all together yet, but that is JUST around the corner. At some point he will want to put it where everyone else does, in the potty. The less pressure he senses from you to do so, the easier it will be for him to just make use of what you've taught him and what he can do and take control of going to the potty. Continue to clean up a miss as matter of factly as possible- "hey, that's your pee-pee... where does the pee go?... In the potty!" was my usual miss-response, in an I Spy tone, like it is a game...
We made it through moving to the Far East at 17 mo, which I was sure would result in a massive potty strike, but was not even a hiccup. DS is 19 mo and has been taking most of the initiative himself since we got here. The key, I believe, was to be as nonchalant as possible, and at the first sign of him refusing an offer when I knew he had to go, I stopped offering, and let him take the reigns. I still sometimes give a hint: hey there is a potty right there, by the plant, in the corner, etc if he is busy and things look imminent. If he doesn't choose to use it, he doesn't pee on the floor- he knows how long he can hold it. He goes later when he is ready. I don't keep pestering him, because that just makes him irritated with the whole potty business. At some point, he knows better than you what he can do and you have to trust him:).
Good luck!