We had to special order a collar for our bulldog, Brutus, the one on the left:
He kept breaking them or slipping them. Because his neck is so thick we couldn't tighten it much, so he could slide backwards out of almost all collars. The one we have on him now isn't smooth, it's got texture on the inside, so when he tries to back out of it it pulls on his fur a bit, so he stops. Thickest leather collar we could find.
He's actually twice the size of a normal bulldog. 85 pounds of lap dog.
:-) And yeah, training was hard. He's broken several chains, one of them a two ton test chain, which is the stuff hubby uses to lift engines out of cars. He's got an extremely strong neck, and with that face there was no way we could get a muzzle on him. If he wasn't so happy and eager to please, I don't think we could have trained him at all. As it is, he'll sit, heel, and come when we call him, but that's about it. That's all we really needed anyway.