One of mine wears a collar just fine, but Archie The Menace can take them all off. They're not even the break away kind!

Unfortunately, if it is safe enough to prevent choking, then it is going to be fairly easy to get out of. You might try going with a harness, I'd advise an H-style harness over the figure-8 style - hopefully that would be enough support to not choke the cat or break bones in case of getting caught on something. But I'm not entirely sure if that is best. Or try talking to your cat, projecting your emotions very strongly, about why it is important he keeps his collar on. I've found that at least sometimes, that kind of thing helps.

It helped with one cat who was spitting medicine back up after I had given it to her.

It only temporarily helps when I have talks with my orange cat about not chewing on wires. Maybe you will have to keep having the talk with your cat.

They do not necessarily understand the words, but they are keen readers of emotions, so they know when something is important to us.