Despite not being a very big dog Beano is quite strong. When we first got him he had a canvas harness, he didn't like it but the rescue centre where we got him from said he wasn't suitable to wear a collar.
This was because he is bull necked, his neck is as wide as his shoulders and it's only once you get past his ears that he starts to narrow. He has a small pointed face so any collar just slides forward and comes off.
I don't like choke collars so we stuck to the harness when we first got him. I then discovered the half check collars, and that's what he now wears. As Steve has discovered, Beano can quite easily discard his half check collar if he so chooses but he seldom attempts it when he is with me. I do also have the knack of holding his lead in such a way that tightens the collar of he tries to do a Houdini escape with me.
What made me think of this was, as I left the flat today I went to put him on the lead. It was only then that I realised that I hadn't put his collar on when I got up this morning. I knew he'd not return to the flat unwalked so I used the lead, which is flat, as a choke collar. Beano was unbothered by this and wandered around happily on an extended walk.