In reply to marsbar:
Aye, most clasp collars are designed to release after a certain load to prevent the dog being hurt / hung if it snags the collar (a neighbors dog hung it's self by accident years ago - can't imagine the horror of coming home to that!!).
Also they should release if the dog gets snarled up playing - quite a few incidents of dogs getting one half of their jaw through a playmate's collar by accident and while struggling to get free they end up twisting the collar, throttling one dog and breaking the jaw of the other eventually. Horrible.
Release collars are definitely the way for me!
I don't know if this one is designed to slip at a certain load though so perhaps fine in that regard?
Cheers,
Stuart